Overflow Valves

[RVhiker]

My trailer has two fresh water tanks and two overflow hoses that exit out the bottom of the Coroplast bottom. I believe that the purpose of the overflow hoses is to prevent overfilling the tanks and causing them to possibly burst. A problem is that when the tanks are filled, and streams of water are exiting through the overflow hoses, that it seems like the "overflow" lasts far longer than any need to stop overfilling; once filled, we have lost as much as one-third of our water supply on the way to a camping site. This excess "overflow" draining is thought to be by caused by siphoning, or by the trailer not being level on the way to a camping site.

I installed small valves in the end of my two siphon hoses. Obviously when filling tanks these valves need to be open, to prevent over-filling. The question: When is the time to close those valves, to prevent the siphoning action?

[Seann45]

As soon as the tubes start draining shut off the water input then shut off the valve on the tubes..

[dewey02]

Here is what I do with mine.

When to have valves open and why to have them open:
1. When filling, because as the water goes in, the overflow tubes act as a vent to let the air in the tank out. If you have them closed when filling, you can balloon your tanks. This is especially true with a two-tank set up, as the second tank likely has no other vent other than the overflow tube.
2. When set up at your campsite and actively using your FW. Again, the overflow tubes act as an air vent and let air into the tanks as you draw water out. If you just stop along your route while travelling to use the toilet for a flush or two, or run a bit of water, it is OK to leave the valves closed...no harm there, but once you set up camp, open them up.
3. When draining your FW tanks through your FW tank drain - again to let air in as water comes out.

When to have the overflow valves closed and why:
1. When you are done filling, to prevent the siphoning effect.
2. When travelling to prevent the slosh out the overflow tubes effect.

[RVhiker]

My thanks to Seann45 and dewey2; both answers helped.

[TCNashville]

RVhiker, dewey02, can you briefly describe what valves you used, where you purchased them and how they're fastened to the overflow tubes. I really need to do this. I know there's a few threads on this and I'm just being lazy by not doing a Forum search. Thanks, Terry

[RVhiker]

I bought a couple of 1/2 inch plastic ball valves - designed for use with PEX piping - at Home Depot. The overflows were 1/2 inch vinyl hose. A 1/2 inch stainless steel PEX clamp ring barely fit onto the end of each hose. I inserted the valve into the hose, and collapsed the clamp with a standard PEX stainless steel clamp tool.

You might be able to use a small screw clamp - like used on a radiator hose - instead of the PEX clamp but I don't think it would work as well.

[dewey02]

Originally Posted by TCNASHVILLE

RVhiker, dewey02, can you briefly describe what valves you used, where you purchased them and how they're fastened to the overflow tubes. I really need to do this. I know there's a few threads on this and I'm just being lazy by not doing a Forum search. Thanks, Terry

I did something a bit different than RVHiker.
I have twin FW tanks, therefore I have two overflow tubes.
I connected both of those tubes to a larger hose and then ran that hose out to near my FW drain hoses. Then I inserted a standard RV type water valve, so I only have to open/close one valve to control both overflow tubes.