I had to replace the drain valve on my fresh water tank on my camper, went to drain it, the valve knob broke off !..lol. I just went to lowes, bought a reg water valve, some 3/4 black pipe, all fixed, works great. not sure how or why yours does not have a drain valve ?, but try looking all around the tank for a water line going straight down through the floor. my tank is under the bed, I can lift the top up, and get to my fresh water tank, water pump, and hot water tank, everything is right there. I do need to buy me a couple of those lift rods, that wood is heavy for a queen bed..lol.