Slow Drip Under Trailer

[Kevin A]

While camping this weekend, I discovered we had a slow leak under our trailer at the point of our fresh water tank drain hose. The hose is generally covered by the insulation foam on the underside, so it is hard to see the actual source of the drip: drain hose, water tank, or plumbing pipes. The water pump cycles about once every 10 minutes apparently due to a loss of pressure. However, can the pressure drop from a drain hose leak? It would seem to be on the wrong side of the pump. I checked all the internal pipes near the leak spot and they are all dry. Could the drain hose leaking cause the pump to cycle?

[Kevin A]

Also, it didn't seem to drip while a faucet was open and the pump was running.

[k corbin]

start at one end of the line and work you way towards the other end. A q-tip makes a great moisture tester. Grab a big handful of them so you have a fresh one to test each join you come to. Press it against the joint then get in the light and press and roll the end of the q-tip to a piece of white paper to see if there is a moist blot on the paper. Of course there could be a leak in the line itself so save that test for last if you don't find any leaks at the joins.

Any fitting of any kind in a water system can leak. The seals on the pump can also leak. But a lot of experience with RV water systems is not needed to track it down to a specific source. It just takes working methodically and patiently.

A lighted inspection mirror is a great help for working in confined spaces where it is difficult to get a direct view of things. You can find those at any hardware store.

Remember water moves and runs with gravity so the leak could be further of the line that where you find moisture. So be sure you don't just stop at one spot thinking you have discovered the one true source, continue on and do checks at other joints on up the line to see if they are dry. And of course it is always possible to have more than one leak which is one of the reasons plumbing can be frustrating.

[k corbin]

Originally Posted by Kevin A

Also, it didn't seem to drip while a faucet was open and the pump was running.

That is because the open faucet was releasing some of the water pressure, it was no longer a closed system. Pressure release valve = opening the faucet. Closed faucet means the void that is the leak is relieving the pressure. The size of the faucet opening is obviously much larger than the void that is the leak so therefore there is not much pressure at the leak.

You are so stressed by the leak that you are forgetting you can apply analytical thinking to this problem.

[Kevin A]

Thanks for the suggestions. I've been gradually replacing the old rigid plumbing with PEX over the past 4 years. The plumbing under the vanity sink is the tightest spot, though, and the toughest to troubleshoot. Mirrors help!

Back to my original question: Can a leaking pipe or tank on the incoming (inlet) side of the pump cause a slow loss of pressure, thus cycling the pump? Or is the only pressure that holds the pump from running on the outlet (faucet) side?

[Dave Fish]

From your description, I would start at the pressurised side of the pump and work outward from there. Water can travel a long ways before it finds an exit. I suspect that the reason you are seeing the wet area by the drain is because that is the low point where it can exit the body.

[Kevin A]

Thanks. It does sound like more of the old pipe joints failing. I'm going to hook up to city water at home and test for a leak, too. That would help ID a possible pump leak if the pipes don't leak from the city hookup.

[jon carpenter]

A check valve may occasionally have debris in it which prevents it from correctly working. Hence, water may flow backwards and the line looses pressure at which time the pump kicks in again. Perhaps inspect the check valve. Don't ask me how I know...LOL

[Radar1]

Based on the pump coming on intermittently, that would indicate a leak on the pressurized side of the pump. A leak in the supply lines to the pump, or a fresh water tank leak would not cause the pump to come on by itself.