Can I set Trash to completely delete certain old files automatically?

Emptying the Trash is a one-click operation. You are trying to dramatically complicate this simple task. Why?

 

i can see this being done with a script that deletes all files of a certain 'age', scheduled to run every night (or whatever) with cron. the script could run something like

Code:

#!/bin/bash

cd /Users/[your-name]/.Trash
rm -v `find . -mtime -2` >> /Users/[your-name]/logfile.txt

exit 0

then have this script run by cron every night - it will delete all files from the trash that were created the previous day.

not positive that this would be so easy (there could be something i'm overlooking), but here are some resources to help you out

http://adminschoice.com/crontab-quick-reference

 

I would recommend software called "Hazel". It's sort of like super-powered Folder Actions, but has a built-in Trash management component that does exactly what you're asking about. It's developed by Noodlesoft.