Upon reaching the campground, we filled up the fresh water tank until water came out of the overflow pipe. Moving to the campsite, water continued to come out (we figured too full over uneven ground, the water will run out).At the campsite, we started to set up and when almost finished and pulling out the awning, I heard an unusual air sound from underneath the camper, overflow pipe most likely. Water had continued to run out of the overflow pipe while we were setting up and the fresh water tank was now down to under 25% full. On prior trips, we had filled the fresh water tank until water came out of the overflow pipe without any problems.What caused the fresh water tank to drain itself through the overflow pipe?We didn't want to undo our work and move the camper back to a fill location, so we used our backup water filler. This is a 5 gallon bucket with a lid, a pond pump, and a special hose to connect to our water supply. After about 5 trips, we had the water tank filled to 100%. It did not give us any problems for the week, and the water system worked as it should.

Sounds like you had a large air pocket that got trapped in your tank.

Sometimes that overflow works like a siphon - and once it gets started, it's hard to stop. We've had it siphon out a half-tank while rolling with a full tank - apparently it sloshed into active as we rolled.Just one of those things.al

Next time, open one of your faucet's in your unit, if the siphoning is happening, this procedure should induct air into your tank, thus stopping your water loss.

Our old Sierra used to siphon the fresh water tank out out of the overflow line. I finally put a valve on the overflow line. Close the valve after the tank is full. Then open it after we had used some water. The tank still had a vent on it, so no worries about collapsing the tank.

I have lost a small amount due to sloshing when moving, but nothing like that. It would seem that if the overflow pipe was higher than the tank,siphoning would not occur.how high up is your overflow hose?

Fresh water tank dumps itself through overflow pipe, why?

powderman426
Explorer
Aug 22, 2013
tenbear wrote:
My overflow attaches to the tank within the top inch of the tank and AFAIK does not extend into the tank. There is no way it could siphon water out, or have water pushed out by trapped air.

Is it possible that you are confusing the drain pipe with the overflow?
yep.thats the way mine is. And the hose breathes just above the fill spout. So all I can lose is whatever sloshes up into the hose.the locking cover prevents anything from entering.
dougrainer
Nomad
Aug 22, 2013
tenbear wrote:
My overflow attaches to the tank within the top inch of the tank and AFAIK does not extend into the tank. There is no way it could siphon water out, or have water pushed out by trapped air.

Is it possible that you are confusing the drain pipe with the overflow?

The fitting does NOT have to extend into the tank to have a faulty vent system that will siphon water out. Doug
tenbear
Explorer
Aug 22, 2013
My overflow attaches to the tank within the top inch of the tank and AFAIK does not extend into the tank. There is no way it could siphon water out, or have water pushed out by trapped air.

Is it possible that you are confusing the drain pipe with the overflow?
dougrainer
Nomad
Aug 22, 2013
The problem is caused by NOT having an equalized air vent system. When you fill and use a pressure fill system, the water tank requires a way to allow fresh air in the tank to be expelled. IF that vent is blocked by the design of the tank and all you do is expelling air, but NO Fresh Air can equalize, when you stop the tank will siphon all the water back out and in extreme cases actually collapse the tank itself. Depending on the design and fittings on the tank will be dependant on what the fix is. Doug
dougrainer
Nomad
Aug 22, 2013
mpfireman wrote:
Next time, open one of your faucet's in your unit, if the siphoning is happening, this procedure should induct air into your tank, thus stopping your water loss.

HOW can this do anything. The faucets on on the pressure side of the water system and the water tank is on the NON pressure side??????? Doug
schlep1967
Nomad
Aug 22, 2013
If your tank drained down to 1/4, odds are that is how far your overflow tube is inserted into the tank. This causes 2 problems. First one is that once you get that much water in, there is no where for the air to escape to. So as you fill the tank you are pressurizing it by compressing the air above the water. Then the 2nd problem happens. You have pressure pushing the water out the tube to equalize the pressure.
You will want to shorten the hose inside the tank.
rbturner
Explorer
Aug 22, 2013
When we owned a 28 foot, 2000 HR Alumalite; we had the same trouble. I was told that they put the overflow tube into the tank too far.

As suggested here, once it starts to syphon out you must stop it or it will run you down to about a quarter tank like you already found out. Ours was repaired under warranty.
JesLookin
Explorer
Aug 22, 2013
Our overflow hose hug out the bottom of the camper. That was probably part of the problem. With the bottom enclosed, it is hard to fine a way to reroute the hose. That is why I took the easy way out & put in the valve.
powderman426
Explorer
Aug 22, 2013
I have lost a small amount due to sloshing when moving, but nothing like that. It would seem that if the overflow pipe was higher than the tank,siphoning would not occur.how high up is your overflow hose?
JesLookin
Explorer
Aug 22, 2013
Our old Sierra used to siphon the fresh water tank out out of the overflow line. I finally put a valve on the overflow line. Close the valve after the tank is full. Then open it after we had used some water. The tank still had a vent on it, so no worries about collapsing the tank.