Reminds me of one of the first times we had our trailer out and there was no sewer hookup. We ran into friends that had been there 3+ days and did not have a problem running out of room in their tanks. I had been looking at the grey water level indicator and it started to say "FULL" after a day or so... Thinking that the indicators are "always off" we continued to fill the grey water tank... I can tell you that if you fill it too much your bath tub will take over the duties of the tank! ( at least in my trailer ). I forgot to mention that my friends were seasoned campers and we were new to the whole tank thing (a much older tent trailer previously) Needless to say we have become water conservers now... although my young children still need alot of prompting! We can go 3-4 days no problem now. I've wondered why they would not put a 20 gallon toilet tank along with a 40 gallon grey water tank. this would make more sense to me since I am forever filling the black water tank before we leave!