When my boa defecates, it looks like a mastiff has been inside her tub. I just take the whole thing outside(it's a VE-175 from reptile tubs) and scrub it with dish soap.

For the chlorhexidine, I usually use 2-3 oz per gallon. Safe to spray on the snake at the concentration too. Mine usually get a wipedown if there is poo present in their tub. Icky little things, LOL.