Ok, I've got three cats which equates to a lot of waste. Currently, I use biodegradable litter box liners, but I'm not sure what to do about the in-betweens.

I change the litter about once a month on average and the liners are actually like their own trash bags. But, throughout the month I've been using the plastic bags from the grocery store to clean out the waste. I have no clue how to make this a more green process. Any ideas?