A lot of people seem to think it is ok to leave the grey tank "open"? First, if you leave the grey tank open, you leave a way for bugs and other creatures to crawl up into your tank. This will cause problems. Two, when washing dishes, even if you are careful, garbage will be washed into the tank. Over time this garbage will build up in the grey tank, and rot! Ever been in a city when there was a garbage pick up strike? Not pretty, and in some ways a worse smell than from your black tank. Third, the water in the grey tank tends to be soapy, from dish washing, hand washing showers, and shampoos. I use this to my advantage, by draining the black tank first, then draining the grey tank. It helps clean the plumbing with the soapy water. BTW, the tanks, both black and grey are called "holding tanks"! There is a reason they are called holding tanks, it is because they are designed, engineered, and manufactured to HOLD there contents until dumped! When you pick up your fiver, you will do a walk thru, pay attention take notes, have someone video it if possible. During this PDI, make sure they show you how to connect the sewer hose, which valve is for the black tank, and which is for the grey tank. It is only a 5 or 10 minuet "drill" that you will have to do at least once a week, but it is no big deal! Good luck on your purchase!