How about some sort of recycle bin? Instead of liquidating (is that the right word?) your unwanted items, you put them in the bin and other characters can take them!

Maybe to get people to do it, you could get paid for recycling. Not as much as liquidating them, though. Or different rewards for the amount you've recylced. Like 1000 recycled gives you a special item (janitor hat, outfit, broom, mop, plunger launcher, etc) or money, and so does 5000, and so on. Maybe even different rewards for different amounts of each color. For example:
1000 grey = 1k
1000 white = 5k
1000 orange = 10k
1000 green = 20k
1000 purple = 50k
1000 pink = 100k
Something like that.

And maybe a limit on taking the recycled items, like 1 or 2 per day. Or maybe you'd have to pay to have access to it.

Anyway, just an idea. Comment please.
Thanks.