Infamous Fresh water tank overflow vent

[Cuda67bnl]

After a few short trips in the coach, I decided it was time to address the apparently common issue of losing fresh water from the front overflow/vent. I just removed the screened fitting at the bottom of the vent line. Then crimped an elbow on, and ran more pex over to the outside edge of the basement, and back to the wet bay. Crimped on a ball valve, and then an elbow with the screened end on it. I did some searching, and read where folks have added valves, check valves, etc, for this issue. Didn’t find much picture wise, just mostly written descriptions. Does anyone see an issue with this? Losing the water isn’t a big deal if you’re headed somewhere with hook ups. But I prefer to arrive with a full tank, and will be doing a lot of dry camping.

[Podivin]

I'm not understanding what I'm seeing - maybe I'm not seeing it correctly. It looks to me that your new pipe comes out of the bottom of the tank. If that's true then how can that be either a vent or an overflow line, both of which are at the top of the tank.

[dbircky]

Doesn’t look like a vent or overflow. Having a valve on either defeats the purpose. I’ve also never seen such an arraignment on a coach, but my guess is it was added as a way to drain the fresh water tank via a hose instead of just dumping the water on the ground.

[wolfe10]

A ball valve on the fresh water tank is OK, but you HAVE to know when to use it.


If you mistakenly leave it closed when using the water pump, you will create a vacuum in the tank. Worse, the pump is strong enough that it would not be out of the question for it to break the tank (collapse it).


That valve should ONLY be closed with you are driving and opened the minute you stop.


And, if traveling with less than a full tank of water, no need to close it. The only time we ever drove with the extra weight of a full water tank was when we were going to dry camp.

[Theturboman]

I understand what the OP is complaining about I filled my tank a few weeks ago all the way up for the first time and I stopped because I saw water coming from under the Moho, figured it was the overflow/vent telling me it was full. Well that son of a gun drained for 10 minutes full stream. I was dry camping so I was a little concerned

[Podivin]

I understand the issue also. What I don't understand is how adding a valve to a line on the BOTTOM of the tank is supposed to help with the overflow taking too much water out of the tank.

[Cuda67bnl]

Originally Posted by Podivin

I understand the issue also. What I don't understand is how adding a valve to a line on the BOTTOM of the tank is supposed to help with the overflow taking too much water out of the tank.

Pretty simple actually. It’s not at the bottom of the tank. The overflow/vent line comes out the top of the tank on the side, turns down, and exits the basement floor. If it didn’t, the basement would get soaked when it overflows…..

Alpines have 2 vent lines on the fresh water tank. One in the front, and one in the rear. The rear one is installed in the top of the tank, loops upwards, then exits the floor of the wet bay. The front one will drain half your water if it ever starts siphoning out. All I did was extend the line, and install a valve. I can now fill the tank completely full, and shut the valve, which prevent the tank from draining while driving. I put the valve at the wet bay, so it’s easy to remember to open it when I get where I’m going.

Most folks who have done something similar, say the rear vent is sufficient on its own. But I intend to open this one once parked. Once the water level has dropped enough, losing water while driving isn’t an issue. I can fill my tank full, stop at the bottom of my driveway, which is fairly steep, and it will start running out the front vent. It’ll suck 10 to 20 gallons before it stops.

[Jeep401]

It only took me about two trips as well to fix the problem. I kept mine a little simpler by just coming over the propane tank bay.
With two vents you probably never need to open this one, but I do anyway. I just reach under the door.
The large fresh water tank was one of many selling points for me because I'm almost always without hookups. So losing a bunch while on the road wasn't going to work for me.
I thought I had posted this before but maybe not. So here you go, another set of pictures.

[Cuda67bnl]

I started to do mine that way. But decided to run it back to the wet bay so it would be right there while I’m filling tank. I can fill til it runs out, then just reach down to shut the valve without having to open another bay.

[Kid Gloves]

Originally Posted by Cuda67bnl

I started to do mine that way. But decided to run it back to the wet bay so it would be right there while I’m filling tank. I can fill til it runs out, then just reach down to shut the valve without having to open another bay.

I’d rotate that ball valve 90, so that the handle moves on the horizontal axis and doesn’t extend down. Or replace it with a smaller PEX valve. I went bare minimum on ours and just cut an inch or so off the tube, added an elbow and a valve. Yes, I have to assume the position to open or close the valve. When that gets old, I’ll probably extend the valve to the propane bay.

Another potential source of water loss is a leaky tank dump valve. Ours recently developed that condition. While installing the new valve, I cut a bit off the drain tube and glued on a slip to threaded fitting. If the valve ever leaks, I can screw on a cap to prevent water loss until a convenient time presents itself for replacement.

[Terry W]

Originally Posted by Cuda67bnl

I started to do mine that way. But decided to run it back to the wet bay so it would be right there while I’m filling tank. I can fill til it runs out, then just reach down to shut the valve without having to open another bay.

I did the same thing, ran it into the corner of the wet bay and straight down. Put a valve in the down pipe and fill the tank til it overflows, shut off the water, close the valve and done. The overflow runs out of the wet bay drain.

When we get set up I leave the valve closed until I figure we’ve used enough water to keep it from siphoning and then open the valve. The top vent has been adequate but I still open the valve just in case.

Terry

[Cuda67bnl]

Originally Posted by Kid Gloves

I’d rotate that ball valve 90, so that the handle moves on the horizontal axis and doesn’t extend down. Or replace it with a smaller PEX valve. I went bare minimum on ours and just cut an inch or so off the tube, added an elbow and a valve. Yes, I have to assume the position to open or close the valve. When that gets old, I’ll probably extend the valve to the propane bay.

Another potential source of water loss is a leaky tank dump valve. Ours recently developed that condition. While installing the new valve, I cut a bit off the drain tube and glued on a slip to threaded fitting. If the valve ever leaks, I can screw on a cap to prevent water loss until a convenient time presents itself for replacement.

I don’t think the valve handle being down would ever be an issue. But I did bend it up.
My dump valve drips every now and then. I think it’s actually getting better. The fitting for a cap is a great idea. I’ll definitely do that in the future.

[Old Scout]

As Brett mentioned, the key is to ensure you open the valve at your destination--dont trust the rear vent to protect the tank. Dont ask me how I know this--oops!

[Cuda67bnl]

Decided to replace the seals in the dump valve, and discovered a weep in the tank where the fitting is friction welded to it. Attempted a repair twice, with a soldering iron, to no avail. So, out it came…….. hopefully I can do a better job now that I won’t be working upside down……