1990 six pac camper sc100

In my 1986 Six-Pac SC100 there is a drain plug lower left/front side of the tank as you're looking at it. Attached is like 8' of clear hosing with a clamp at the end. I snake that out the back, suck on it just enough to get it flowing and let it do it's thing. I don't know if a previous owner added that or not. It gets all, but maybe 1/2 gallon at the bottom. I usually throw a pinch of bleach in there to keep everything at bay if it's sitting for awhile.

As a water capacity test I ran the pump for 15 minutes straight once without a problem, but it did get HOT.