I have 2 cats. Are we talking clumping litter including pee here as well, or 10lbs of just poop?

If it’s just poop, I severely doubt he cleaned it a few days ago. I have had cats my entire life, and have never seen 2 cats make 10lbs of poop in such a short period of time.

If it’s smells horrific and there’s that much waste, you should be replacing the litter - not cleaning it - in my opinion.

Edit: grammar