Have you crawled under the trailer yet. Easiest way to find it. On our HH the fresh water tank was just rear of the rear axle. A black pipe was hanging down. If you slide your hand up it there was a valve. If you turn the valve and it does not drain there's a good chance a mud dauber built a nest up in it. I used a bamboo screwer to poke around and get it running. Once it starts your good to go.