Two of those valves are probably for actually filling the (one) potable water tank , one valve for filling the tank and the other when you are hooked to campground water source and the other valves are for draining the water tank the hot water tank and the lines, the water tank has a dump line that spills water on the ground when the tank is full.
The grey and the black tank have handles on the black PVC pipes located under the RV, these tanks are filled as you use the potable water, when dumping first open the black tank valve, big pipe and after all the "water" has emptied then open the gray water tank valve, small pipe, that way you "clean" the sewer hose from toilet sludge.
Word of caution do not put anything in the toilet that you did not eat other than toilet paper, and do not waste money in marine and RV toilet paper, use Costco instead they really dissolve fast.
navegator
