Water leak from fresh water tank

Awesome post!
Thanks, Chris Beierl for all the details!

Here's the Plumbing Diagram for your coach. Unfortunately, this valve isn't shown very well on the diagrams. The pipe you are referring to is the fresh water tank drain, controlled via a cable operated blade valve. This valve is described on page 88 of the Operator's Manual for your coach.

Here's the Parts Catalog for your coach. You can see the valve on page 262.

Here's a replacement valve for that drain:
Valterra T1001PBC 1-1/2" Valve Body

Here's a replacement seal kit: Valterra T1001-9VP Bladex 1-1/2" Valve Seal with Hardware, (Set of 2)

I just replaced that valve on my 2005 Vectra last year because it developed a leak--I initially replaced just the seals, but ended up replacing the entire valve because I still had a leak (so now I have the spare seals available for next time). On my coach access was straightforward from underneath, after removing the insulated sheet metal panel from under the water tank. (I made some large wooden ramps/blocks to drive the front of the coach up onto to give me adequate height to work safely underneath without danger.)

wrgrs50s wrote:
Sounds like the pipe your referring to is your overflow tube for your freshwater tank.

It's possible that your City water fill valve may be malfunctioning and allowing a small amount of water to bypass into your freshwater tank overfilling slowly to the point of it seeping out the overflow. Also, the check valve built in to your water pump can go bad and allow water back into your FW tank when on city water. The best way to tell if either of these is your problem is to totally drain your Fresh tank and then monitor your guages when connected to city water and see if the tank is slowly rising, or just leave the valve open to your freswater drain and watch for a slow drip while connected to city water. Both ways will verify you have water feeding back while on city water.

The way I read the OP he is having trouble with water leaking OUT of the FW tank. Not water leaking IN to the FW tank. Am I reading it wrong?

I don't have your particular model motorhome and I am not specifically familiar with it but it does sound like a failed or open tank drain valve to me. Possibly the fitting where the tank drain is connected to the tank.

Thanks for the tips!

Sounds like the pipe your referring to is your overflow tube for your freshwater tank.

It's possible that your City water fill valve may be malfunctioning and allowing a small amount of water to bypass into your freshwater tank overfilling slowly to the point of it seeping out the overflow. Also, the check valve built in to your water pump can go bad and allow water back into your FW tank when on city water. The best way to tell if either of these is your problem is to totally drain your Fresh tank and then monitor your guages when connected to city water and see if the tank is slowly rising, or just leave the valve open to your freswater drain and watch for a slow drip while connected to city water. Both ways will verify you have water feeding back while on city water.

I have had good luck fixing leaks in plastic tanks with Shoe Goo. Not much will chemically bond to ABS type plastics but if you rough up the surface around the crack and dry the area well you can get a good mechanical bond to the plastic tank using Shoe Goo.

It’s probably the low point drain for the tank. There should be a valve somewhere between the tank and that pipe that may be partly open or leaking. You should not have to remove any panels to see the valve although you likely will need to look hard.