Mark-k

Once a day wordpress deletes all trashed items which had been in the trash for more then N days, where N stands for the value of EMPTY_TRASH_DAYS constant which may be defined in wp-config.php file.
This plugin presents a different way to control the number of trashed days. Instead of manually editing wp-config.php which is usually not convenient and somewhat dangerous, you can set the number of days in a settings page. 
In addition there is a tool to empty the cache from Items older the a specified number of days.
Usage: 
Get to the settings page via the menu “Options” >> “Empty trash” 
Get to the delete trash tool page via the menu “Tools” >> “Empty trash”
Network considerations: 
The plugin was not tested in a network installation, but it should work gibing the individual site admin a control over his trash which is possibly different then other sites on the network. 
The plugin do not have network wide settings
Important: 
For better or worse the plugin employs exactly the same deleting algorithm used by the wordpress version running the site.
Limitations: 
The plugin will not be able to function well if you have EMPTY_TRASH_DAYS set in your wp-confing.php

Trash emptier

Provides a configurable control over the trash emptying algorithm wordpress uses without changing wp-config.php

saadibrahim

Plugin for WordPress that adds a notice in dashboard about WordPress automatically removing trashed posts after 30 days. Helpful for developers with lots of clients and sites with lots of editors.
It adds the notice to the message that appear when you trash an item and also shows the notice on the trashed post table. It works with all custom post types and pages as well. It also check if you have changed the number of days posts are deleted from trash.
I created this plugin after a client complained that she didn’t know that WordPress would automatically delete the post.

Trash Notice

Plugin for WordPress that adds a notice in dashboard about WordPress automatically removing trashed posts…

Trash emptier vs Trash Notice