diff --git a/_config/requestprocessors.yml b/_config/requestprocessors.yml
index 1e9310bd3..17ee24025 100644
--- a/_config/requestprocessors.yml
+++ b/_config/requestprocessors.yml
@@ -5,4 +5,5 @@ Injector:
   RequestProcessor:
     properties:
       filters:
+        - '%$FlushRequestFilter'
         - '%$VersionedRequestFilter'
diff --git a/api/RestfulService.php b/api/RestfulService.php
index 5f8d7ae29..9d1116d42 100644
--- a/api/RestfulService.php
+++ b/api/RestfulService.php
@@ -9,7 +9,7 @@
  * @package framework
  * @subpackage integration
  */
-class RestfulService extends ViewableData {
+class RestfulService extends ViewableData implements Flushable {
 
 	protected $baseURL;
 	protected $queryString;
@@ -33,6 +33,19 @@ class RestfulService extends ViewableData {
 	 */
 	private static $default_curl_options = array();
 
+	/**
+	 * @config
+	 * @var bool Flushes caches if set to true. This is set by {@link flush()}
+	 */
+	private static $flush = false;
+
+	/**
+	 * Triggered early in the request when someone requests a flush.
+	 */
+	public static function flush() {
+		self::$flush = true;
+	}
+
 	/**
 	 * set a curl option that will be applied to all requests as default
 	 * {@see http://php.net/manual/en/function.curl-setopt.php#refsect1-function.curl-setopt-parameters}
@@ -171,7 +184,7 @@ class RestfulService extends ViewableData {
 		// Check for unexpired cached feed (unless flush is set)
 		//assume any cache_expire that is 0 or less means that we dont want to
 		// cache
-		if($this->cache_expire > 0 && !isset($_GET['flush'])
+		if($this->cache_expire > 0 && self::$flush
 				&& @file_exists($cache_path)
 				&& @filemtime($cache_path) + $this->cache_expire > time()) {
 			
diff --git a/control/FlushRequestFilter.php b/control/FlushRequestFilter.php
new file mode 100644
index 000000000..ab6be8dd4
--- /dev/null
+++ b/control/FlushRequestFilter.php
@@ -0,0 +1,24 @@
+<?php
+/**
+ * Triggers a call to flush() on all implementors of Flushable.
+ *
+ * @package framework
+ * @subpackage control
+ */
+class FlushRequestFilter implements RequestFilter {
+
+	public function preRequest(SS_HTTPRequest $request, Session $session, DataModel $model) {
+		if($request->getVar('flush')) {
+			foreach(ClassInfo::implementorsOf('Flushable') as $class) {
+				$class::flush();
+			}
+		}
+
+		return true;
+	}	
+
+	public function postRequest(SS_HTTPRequest $request, SS_HTTPResponse $response, DataModel $model) {
+		return true;
+	}
+
+}
diff --git a/control/RequestProcessor.php b/control/RequestProcessor.php
index e391be0a5..566ad8017 100644
--- a/control/RequestProcessor.php
+++ b/control/RequestProcessor.php
@@ -45,4 +45,4 @@ class RequestProcessor implements RequestFilter {
 			}
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/core/Flushable.php b/core/Flushable.php
new file mode 100644
index 000000000..4b1781bb9
--- /dev/null
+++ b/core/Flushable.php
@@ -0,0 +1,20 @@
+<?php
+/**
+ * Provides an interface for classes to implement their own flushing functionality
+ * whenever flush=1 is requested.
+ *
+ * @package framework
+ * @subpackage core
+ */
+interface Flushable {
+
+	/**
+	 * This function is triggered early in the request if the "flush" query
+	 * parameter has been set. Each class that implements Flushable implements
+	 * this function which looks after it's own specific flushing functionality.
+	 *
+	 * @see FlushRequestFilter
+	 */
+	public static function flush();
+
+}
diff --git a/dev/TestRunner.php b/dev/TestRunner.php
index 4c8d9e1c1..8cd57b6fe 100755
--- a/dev/TestRunner.php
+++ b/dev/TestRunner.php
@@ -49,7 +49,7 @@ class TestRunner extends Controller {
 		'build',
 		'only'
 	);
-	
+
 	/**
 	 * @var Array Blacklist certain directories for the coverage report.
 	 * Filepaths are relative to the webroot, without leading slash.
@@ -62,7 +62,7 @@ class TestRunner extends Controller {
 		'*/tests',
 		'*/lang',
 	);
-	
+
 	/**
 	 * Override the default reporter with a custom configured subclass.
 	 *
@@ -78,21 +78,26 @@ class TestRunner extends Controller {
 	 * top of the loader stacks.
 	 */
 	public static function use_test_manifest() {
+		$flush = true;
+		if(isset($_GET['flush']) && $_GET['flush'] === '0') {
+			$flush = false;
+		}
+
 		$classManifest = new SS_ClassManifest(
-			BASE_PATH, true, isset($_GET['flush'])
+			BASE_PATH, true, $flush
 		);
-		
+
 		SS_ClassLoader::instance()->pushManifest($classManifest, false);
 		SapphireTest::set_test_class_manifest($classManifest);
 
 		SS_TemplateLoader::instance()->pushManifest(new SS_TemplateManifest(
-			BASE_PATH, project(), true, isset($_GET['flush'])
+			BASE_PATH, project(), true, $flush
 		));
 
 		Config::inst()->pushConfigStaticManifest(new SS_ConfigStaticManifest(
-			BASE_PATH, true, isset($_GET['flush'])
+			BASE_PATH, true, $flush
 		));
-		
+
 		// Invalidate classname spec since the test manifest will now pull out new subclasses for each internal class
 		// (e.g. Member will now have various subclasses of DataObjects that implement TestOnly)
 		DataObject::clear_classname_spec_cache();
@@ -109,14 +114,6 @@ class TestRunner extends Controller {
 		if(!PhpUnitWrapper::has_php_unit()) {
 			die("Please install PHPUnit using pear");
 		}
-
-		if(!isset($_GET['flush']) || !$_GET['flush']) {
-			Debug::message(
-				"WARNING: Manifest not flushed. " .
-				"Add flush=1 as an argument to discover new classes or files.\n",
-				false
-			);
-		}
 	}
 	
 	public function Link() {
diff --git a/docs/en/howto/phpunit-configuration.md b/docs/en/howto/phpunit-configuration.md
index 4ac184feb..92db5bfbe 100644
--- a/docs/en/howto/phpunit-configuration.md
+++ b/docs/en/howto/phpunit-configuration.md
@@ -76,17 +76,31 @@ Example `mysite/_config.php`:
 			if($db == 'sqlite3') $databaseConfig['type'] = 'SQLite3Database';
 		}
 	}
-	
+
 You can either use the database on a single invocation:
 
 	phpunit framework/tests "" db=sqlite3
-	
+
 or through a `<php>` flag in your `phpunit.xml` (see [Appenix C: "Setting PHP INI settings"](http://www.phpunit.de/manual/current/en/appendixes.configuration.html)):
 
 	<phpunit>
 		<!-- ... -->
 		<php>
-			<var name="db" value="sqlite3"/>
+			<get name="db" value="sqlite3"/>
+		</php>
+	</phpunit>
+
+Note that on every test run, the manifest is flushed to avoid any bugs where a test doesn't clean up after
+itself properly. You can override that behaviour by passing `flush=0` to the test command:
+
+	phpunit framework/tests flush=0
+
+Alternatively, you can set the var in your `phpunit.xml` file:
+
+	<phpunit>
+		<!-- ... -->
+		<php>
+			<get name="flush" value="0"/>
 		</php>
 	</phpunit>
 
diff --git a/docs/en/reference/execution-pipeline.md b/docs/en/reference/execution-pipeline.md
index 7359a8a3e..1f5175fee 100644
--- a/docs/en/reference/execution-pipeline.md
+++ b/docs/en/reference/execution-pipeline.md
@@ -93,3 +93,12 @@ You can access the following controller-method with /team/signup
 ## SSViewer template rendering
 
 See [templates](/reference/templates) for information on the SSViewer template system.
+
+## Flush requests
+
+If `?flush=1` is requested in the URL, e.g. http://mysite.com?flush=1, this will trigger a call to `flush()` on
+any classes that implement the `Flushable` interface.
+
+See [reference documentation on Flushable](/reference/flushable) for more details.
+
+
diff --git a/docs/en/reference/flushable.md b/docs/en/reference/flushable.md
new file mode 100644
index 000000000..b24634c57
--- /dev/null
+++ b/docs/en/reference/flushable.md
@@ -0,0 +1,56 @@
+# Flushable
+
+## Introduction
+
+Allows a class to define it's own flush functionality, which is triggered when `flush=1` is requested in the URL.
+
+`[api:FlushRequestFilter]` is run before a request is made, calling `flush()` statically on all
+implementors of `[api:Flushable]`.
+
+## Usage
+
+To use this API, you need to make your class implement `[api:Flushable]`, and define a `flush()` static function,
+this defines the actions that need to be executed on a flush request.
+
+### Using with SS_Cache
+
+This example uses `[api:SS_Cache]` in some custom code, and the same cache is cleaned on flush:
+
+	:::php
+	<?php
+	class MyClass extends DataObject implements Flushable {
+	
+		public static function flush() {
+			SS_Cache::factory('mycache')->clean(Zend_Cache::CLEANING_MODE_ALL);
+		}
+	
+		public function MyCachedContent() {
+			$cache = SS_Cache::factory('mycache')
+			$something = $cache->get('mykey');
+			if(!$something) {
+				$something = 'value to be cached';
+				$cache->save($something);
+			}
+			return $something;
+		}
+	
+	}
+
+### Using with filesystem
+
+Another example, some temporary files are created in a directory in assets, and are deleted on flush. This would be
+useful in an example like `GD` or `Imagick` generating resampled images, but we want to delete any cached images on
+flush so they are re-created on demand.
+
+	:::php
+	<?php
+	class MyClass extends DataObject implements Flushable {
+	
+		public static function flush() {
+			foreach(glob(ASSETS_PATH . '/_tempfiles/*.jpg') as $file) {
+				unlink($file);
+			}
+		}
+	
+	}
+
diff --git a/docs/en/topics/caching.md b/docs/en/topics/caching.md
index 26c8d55e4..91a08140d 100644
--- a/docs/en/topics/caching.md
+++ b/docs/en/topics/caching.md
@@ -98,6 +98,13 @@ this is reasonably quick, but still requires access to slow disk I/O.
 The `Zend_Cache` API supports various caching backends ([list](http://framework.zend.com/manual/1.12/en/zend.cache.backends.html))
 which can provide better performance, including APC, Xcache, ZendServer, Memcached and SQLite.
 
+## Cleaning caches on flush=1 requests
+
+If `?flush=1` is requested in the URL, e.g. http://mysite.com?flush=1, this will trigger a call to `flush()` on
+any classes that implement the `Flushable` interface. Using this, you can trigger your caches to clean.
+
+See [reference documentation on Flushable](/reference/flushable) for implementation details.
+
 ### Memcached
 
 This backends stores cache records into a [memcached](http://www.danga.com/memcached/) 
@@ -144,4 +151,4 @@ a fast one (but limited) like Apc, Memcache... and a "slow" one like File or Sql
 				'cache_dir' => TEMP_FOLDER . DIRECTORY_SEPARATOR . 'cache'
 		)
 	));
-	SS_Cache::pick_backend('two_level', 'any', 10); 
\ No newline at end of file
+	SS_Cache::pick_backend('two_level', 'any', 10); 
diff --git a/i18n/i18n.php b/i18n/i18n.php
index 4b81fe1c9..4acc5eb1a 100644
--- a/i18n/i18n.php
+++ b/i18n/i18n.php
@@ -61,7 +61,7 @@ require_once 'i18nSSLegacyAdapter.php';
  * @package framework
  * @subpackage misc
  */
-class i18n extends Object implements TemplateGlobalProvider {
+class i18n extends Object implements TemplateGlobalProvider, Flushable {
 
 	/**
 	 * This static variable is used to store the current defined locale.
@@ -97,6 +97,21 @@ class i18n extends Object implements TemplateGlobalProvider {
 	 */
 	protected static $translators;
 
+	/**
+	 * Triggered early in the request when someone requests a flush.
+	 */
+	public static function flush() {
+		self::get_cache()->clean(Zend_Cache::CLEANING_MODE_ALL);
+	}
+
+	/**
+	 * Return an instance of the cache used for i18n data.
+	 * @return Zend_Cache
+	 */
+	public static function get_cache() {
+		return SS_Cache::factory('i18n', 'Output', array('lifetime' => null, 'automatic_serialization' => true));
+	}
+
 	/**
 	 * Use javascript i18n through the ss.i18n class (enabled by default).
 	 * If set to TRUE, includes javascript requirements for the base library
@@ -2039,11 +2054,11 @@ class i18n extends Object implements TemplateGlobalProvider {
 				// which is instanciated by core with a $clean instance variable.
 
 				if(!$adapter->isAvailable($lang)) {
-					i18n::include_by_locale($lang, (isset($_GET['flush'])));
+					i18n::include_by_locale($lang);
 				}
 
 				if(!$adapter->isAvailable($locale)) {
-					i18n::include_by_locale($locale, (isset($_GET['flush'])));
+					i18n::include_by_locale($locale);
 				}
 
 				$translation = $adapter->translate($entity, $locale);
@@ -2107,9 +2122,7 @@ class i18n extends Object implements TemplateGlobalProvider {
 	 */
 	public static function get_translators() {
 		if(!Zend_Translate::getCache()) {
-			Zend_Translate::setCache(
-				SS_Cache::factory('i18n', 'Output', array('lifetime' => null, 'automatic_serialization' => true))
-			);
+			Zend_Translate::setCache(self::get_cache());
 		}
 
 		if(!self::$translators) {
@@ -2122,8 +2135,8 @@ class i18n extends Object implements TemplateGlobalProvider {
 				))
 			);
 
-			i18n::include_by_locale('en', isset($_GET['flush']));
-			i18n::include_by_locale('en_US', isset($_GET['flush']));
+			i18n::include_by_locale('en');
+			i18n::include_by_locale('en_US');
 		}
 
 		return self::$translators;
@@ -2515,7 +2528,7 @@ class i18n extends Object implements TemplateGlobalProvider {
 	 */
 	public static function include_by_locale($locale, $clean = false) {
 		if($clean) {
-			Zend_Translate::clearCache();
+			self::flush();
 		}
 
 		// Get list of module => path pairs, and then just the names
diff --git a/model/Image.php b/model/Image.php
index f08bc3a16..d1b41903f 100644
--- a/model/Image.php
+++ b/model/Image.php
@@ -6,7 +6,7 @@
  * @package framework
  * @subpackage filesystem
  */
-class Image extends File {
+class Image extends File implements Flushable {
 	
 	const ORIENTATION_SQUARE = 0;
 	const ORIENTATION_PORTRAIT = 1;
@@ -71,11 +71,24 @@ class Image extends File {
 	 * @var bool Force all images to resample in all cases
 	 */
 	private static $force_resample = false;
-	
+
+	/**
+	 * @config
+	 * @var bool Regenerates images if set to true. This is set by {@link flush()}
+	 */
+	private static $flush = false;
+
+	/**
+	 * Triggered early in the request when someone requests a flush.
+	 */
+	public static function flush() {
+		self::$flush = true;
+	}
+
 	public static function set_backend($backend) {
 		self::config()->backend = $backend;
 	}
-	
+
 	public static function get_backend() {
 		return self::config()->backend;
 	}
@@ -424,7 +437,7 @@ class Image extends File {
 		if($this->ID && $this->Filename && Director::fileExists($this->Filename)) {
 			$cacheFile = call_user_func_array(array($this, "cacheFilename"), $args);
 			
-			if(!file_exists(Director::baseFolder()."/".$cacheFile) || isset($_GET['flush'])) {
+			if(!file_exists(Director::baseFolder()."/".$cacheFile) || self::$flush) {
 				call_user_func_array(array($this, "generateFormattedImage"), $args);
 			}
 			
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index bd02b154e..d95e29bbc 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -66,10 +66,3 @@ SapphireTest::set_is_running_test(true);
 // Remove the error handler so that PHPUnit can add its own
 restore_error_handler();
 
-if(!isset($_GET['flush']) || !$_GET['flush']) {
-	Debug::message(
-		"WARNING: Manifest not flushed. " .
-		"Add flush=1 as an argument to discover new classes or files.\n",
-		false
-	);
-}
diff --git a/view/Requirements.php b/view/Requirements.php
index 7db31e0d9..8848c6087 100644
--- a/view/Requirements.php
+++ b/view/Requirements.php
@@ -7,7 +7,14 @@
  * @package framework
  * @subpackage view
  */
-class Requirements {
+class Requirements implements Flushable {
+
+	/**
+	 * Triggered early in the request when someone requests a flush.
+	 */
+	public static function flush() {
+		self::delete_all_combined_files();
+	}
 
 	/**
 	 * Enable combining of css/javascript files.
@@ -272,6 +279,13 @@ class Requirements {
 		return self::backend()->delete_combined_files($combinedFileName);
 	}
 
+	/**
+	 * Deletes all generated combined files in the configured combined files directory,
+	 * but doesn't delete the directory itself.
+	 */
+	public static function delete_all_combined_files() {
+		return self::backend()->delete_all_combined_files();
+	}
 
 	/**
 	 * Re-sets the combined files definition. See {@link Requirements_Backend::clear_combined_files()}
@@ -455,7 +469,7 @@ class Requirements_Backend {
 	 * @var boolean
 	 */
 	protected $force_js_to_bottom = false;
-	
+
 	public function set_combined_files_enabled($enable) {
 		$this->combined_files_enabled = (bool) $enable;
 	}
@@ -1005,6 +1019,20 @@ class Requirements_Backend {
 		}
 	}
 
+	/**
+	 * Deletes all generated combined files in the configured combined files directory,
+	 * but doesn't delete the directory itself.
+	 */
+	public function delete_all_combined_files() {
+		$combinedFolder = $this->getCombinedFilesFolder();
+		if(!$combinedFolder) return false;
+
+		$path = Director::baseFolder() . '/' . $combinedFolder;
+		if(file_exists($path)) {
+			Filesystem::removeFolder($path, true);
+		}
+	}
+
 	public function clear_combined_files() {
 		$this->combine_files = array();
 	}
@@ -1085,7 +1113,7 @@ class Requirements_Backend {
 			}
 
 			// Determine if we need to build the combined include
-			if(file_exists($combinedFilePath) && !isset($_GET['flush'])) {
+			if(file_exists($combinedFilePath)) {
 				// file exists, check modification date of every contained file
 				$srcLastMod = 0;
 				foreach($fileList as $file) {
diff --git a/view/SSViewer.php b/view/SSViewer.php
index d5fc9fba1..f426b3d9c 100644
--- a/view/SSViewer.php
+++ b/view/SSViewer.php
@@ -555,7 +555,7 @@ class SSViewer_DataPresenter extends SSViewer_Scope {
  * <b>Caching</b>
  *
  * Compiled templates are cached via {@link SS_Cache}, usually on the filesystem.  
- * If you put ?flush=all on your URL, it will force the template to be recompiled.  
+ * If you put ?flush=1 on your URL, it will force the template to be recompiled.
  *
  * @see http://doc.silverstripe.org/themes
  * @see http://doc.silverstripe.org/themes:developing
@@ -563,7 +563,7 @@ class SSViewer_DataPresenter extends SSViewer_Scope {
  * @package framework
  * @subpackage view
  */
-class SSViewer {
+class SSViewer implements Flushable {
 	
 	/**
 	 * @config
@@ -638,6 +638,13 @@ class SSViewer {
 	 */
 	private static $global_key = '$CurrentReadingMode, $CurrentUser.ID';
 
+	/**
+	 * Triggered early in the request when someone requests a flush.
+	 */
+	public static function flush() {
+		self::flush_template_cache();
+	}
+
 	/**
 	 * Create a template from a string instead of a .ss file
 	 * 
@@ -744,18 +751,6 @@ class SSViewer {
 	public function __construct($templateList, TemplateParser $parser = null) {
 		$this->setParser($parser ?: Injector::inst()->get('SSTemplateParser'));
 
-		// flush template manifest cache if requested
-		if (isset($_GET['flush']) && $_GET['flush'] == 'all') {
-			if(Director::isDev() || Director::is_cli() || Permission::check('ADMIN')) {
-				self::flush_template_cache();
-			} else {
-				if(!Security::ignore_disallowed_actions()) {
-					return Security::permissionFailure(null, 'Please log in as an administrator to flush ' .
-						'the template cache.');
-				}
-			}
-		}
-		
 		if(!is_array($templateList) && substr((string) $templateList,-3) == '.ss') {
 			$this->chosenTemplates['main'] = $templateList;
 		} else {
@@ -927,7 +922,7 @@ class SSViewer {
 		if (!self::$flushed) {
 			$dir = dir(TEMP_FOLDER);
 			while (false !== ($file = $dir->read())) {
-				if (strstr($file, '.cache')) { unlink(TEMP_FOLDER.'/'.$file); }
+				if (strstr($file, '.cache')) unlink(TEMP_FOLDER . '/' . $file);
 			}
 			self::$flushed = true;
 		}
@@ -1038,7 +1033,7 @@ class SSViewer {
 			. str_replace(array('\\','/',':'), '.', Director::makeRelative(realpath($template)));
 		$lastEdited = filemtime($template);
 
-		if(!file_exists($cacheFile) || filemtime($cacheFile) < $lastEdited || isset($_GET['flush'])) {
+		if(!file_exists($cacheFile) || filemtime($cacheFile) < $lastEdited) {
 			$content = file_get_contents($template);
 			$content = $this->parseTemplateContent($content, $template);