I don't personally breed rats, but once a week I help out a friend who does. Every week tubs get scrubbed with hot water and dish soap. He's had better luck rotating males than doing harems and keeps at most 3 females in a tub. We clean every Tuesday and it smells pretty ripe by then. We use plenty of bedding but in some tubs the ammonia can be a bit intense, especially if it's a tubs with 3 litters of weanlings that need to be pulled. I can't imagine just dumping the bedding and putting more in on top of all the residue that hasn't been cleaned. They may just be feeders but they deserve to live a good life in a clean home. Since there is usually 2-3 of us we've been able to work out an assembly line type system using a few extra tubs. It only takes us 1.5-2 hours to clean 60+ cages. Even doing it alone it doesn't take that much more time to give the tubs a quick scrub with soap and hot water.