Need Help! Dripping water.

[Bluto]

I can't figure this out so I'm asking for some help on this one.

I have a new trailer and when I'm not hooked into city water and am using the water in the tank with the pump here's what happens:

The pump pressurizes the water lines and works normal and I have no leaks. Pump shuts off and does not cycle as it would if a leak is present. When I turn the pump switch off and leave pressure in the lines I get a puddle of water (1/2 cup) under the white box where the city water hook up is located. It just drips out a weep hole in the bottom of the box. It will stop after a puddle forms on the concrete under the trailer. The drip will not happen if I leave the pump in the on position either.
If after I shut down the pump with the switch and drain the pressure out of the lines say by flushing the toilet I get no puddle under the trailer and no dripping from the box.
I just can't figure out why this is happening.
Please give me some ideas on how to find out what is wrong.

[easyride]

Is there a back flow preventer there? they are known to belch a little bit. Dave

[Bluto]

I don't know if there is a back flow preventer. I don't know what one looks like. If it is located in the white box it may be difficult to get into. There are 2 places to hook up hoses and one valve coming out of the box face. One for city water, one for the auto cleanout spray for the black tank and one that is just like an outside spigot to get water from the tank when outside.
I called A/S and spoke to Randy Mcneeley and asked him, but he was no help.
He said that water should not be dripping out, but he did not offer a way to solve the problem.
He sent me a plumbing diagram but that was no help and does not show a back flow preventer. Could the backflo preventer be in the pump itself?

[Bluto]

Ok, another phone call to A/S at Jackson Center. This time I spoke to Rick in the service shop. He has never seen this problem either and says that the white box will have to be taken apart to find the leak (drip). He too says the drip is not supposed to happen. So it must be a leak in the water line someplace. Probably at a connection behind the panel in the white box.
Well at least it's outside the main part of the trailer. Now just to track it down.

Any other ideas out there?