Update, April 6th, 2012: After finding and installing Monique's Auto Tending Compost mod, I found that the original customization wasn't enough anymore; trash stacks up so fast, that you need more capacity, and faster processing. So now there's also a "x2" version, which holds double the amount, and works twice as fast. This new bin holds 100 units, and converts a unit of trash to compost once every 4 hours.
NOTE: You can have only one of these mods in your downloads folder; they both change the same files to alter the properties of the original Maxis Compost Bin, so they conflict with eachother.
Filesize 2.52 KB | File Name BO - Customized Compost Bin x2.zip | # of Downloads 655
This mod was meant to help a little.