Same here as other post!!! DON'T put grease in the drains. over 18 years of RVing and now on our 5ht unit. Never had any issues. Make sure you wipe out all food stuff before washing. A few paper towels are much less costly than cleaners and a lot less aggravating. Yo might try hooking up to your home dump station and using only super hot water, fill up the tank and let is sit a bit heating up the grease to help make it liquid and then flush, flush and keep flushing with HOT water until grease is gone. And like the others say, don't do that ! ! ! Good Luck & Be Safe ! ! !