ksg5000 wrote:
Low point drain valves should have a drain tube that sticks down beneath the floorboards ... if you take a look under the rig you should be able to spot the tubes and locate the approximate location of the valve. Hope this helps.
This ^^^^^^^^^^^^^^^^^^^^^ is the best advice you could get. Every RV has them in a different location. Crawl under and look for 2 rather small (1/2 inch-ish) poly tubes sticking down through the floor. A single larger tube (1 or 1&1/2 inch-ish) is the fresh water tank drain.