Activating Redstone singal when items are in chest

I have buckets with randon fluids in them and i want to get rid of them so i set up a dispenser that pushes the liquid out and set up a piston to destroy but i have to it a lever each time for it to activate the piston and destory it. so if someone could help me write a computer craft code to dectect items in chest then activate a redstone signal that would be nice. Here is a picture of the setup I have.

You could probably acheive this with some openP code, but i have to ask… What are you using to activate the dispenser, and why can't you use the same to activate the piston? Also, it would probably be far easier to just use a BC gate.

or comparator?

I've only heard of this "Comparator" which you speak of, i stopped using vanilla at like 1.2.5 :P/>

Place comparator facing out of any side of dispenser - if there are any items in dispenser it will provide redsone signal - more items stronger signal.
If you place repeater right after comparator it will up signal to max 16 blocks - then use that signal to fire dispenser and piston/

Thank you ill try these and see if they work :)/>

Thanks the comparator trick worked thx ;)/>

Or, if you have Buildcraft installed, you can use a void pipe.

Less noise than a piston…