Fresh Water Tank Overflow and Vent Function

[bigbAZ]

I've always wondered about the fresh water tank overflow. On my motorhome it is a 1.5" pipe that elbows down from the top, wide open. What keeps dust and dirt from getting in the water tank through that pipe? Is it also a vent to relieve suction when drawing down with the pump? Trying to figure out how that would work if it has some kind of two way flapper or something. Or maybe the relief is a separate hose or pipe that terminates in an enclosed area and the overflow has a one way valve?

BTW I reduced mine down to 3/4" and attached a garden hose threaded nipple so I can drain/flush the tank while parked in the garage, but I am reluctant to screw a cap onto it, there has to be a reason it left the factory with no way to close it off.

 

[DonTom]

I've always wondered about the fresh water tank overflow. On my motorhome it is a 1.5" pipe that elbows down from the top, wide open. What keeps dust and dirt from getting in the water tank through that pipe? Is it also a vent to relieve suction when drawing down with the pump? Trying to figure out how that would work if it has some kind of two way flapper or something. Or maybe the relief is a separate hose or pipe that terminates in an enclosed area and the overflow has a one way valve?

BTW I reduced mine down to 3/4" and attached a garden hose threaded nipple so I can drain/flush the tank while parked in the garage, but I am reluctant to screw a cap onto it, there has to be a reason it left the factory with no way to close it off.

I have wondered the same thing. but I never drink the water from the RV tank so I have no need to be concerned, other than perhaps what @Professor David says here.

-Don- Auburn,CA

 

[bigbAZ]

I don't drink it either but I am still curious about how it works. I believe I mis-spoke about the 1.5" pipe, I found some 3D images from Winnebago and that pipe comes from the bottom of the tank and it's where the water drains out when I pull the valve. I have no idea if I even have an overflow, the diagrams don't show anything but the big drain pipe on the bottom and 3 water lines out the top which go under the bed where the pump is, and into the wet bay where the tank fill is. My tank fill is pressurized, not gravity. you screw on the hose firmly then turn the valve to "tank fill" and fill it up. I thought there must be an overflow but I've never filled it all the way to find out. I also thought there has to be a way to let air into the tank to relive suction when drawing water out but I can't see anything. The water seems to be very clean. Guess it will just be a mystery.

 

[Rene T]

Do you have a gravity fill pipe? If you do, usually there is vent next to it to allow air to escape when filling the tank that way. You can find any vent by just open the tank fill valve just a little and watch for water to run out.

 

[bigbAZ]

Do you have a gravity fill pipe? If you do, usually there is vent next to it to allow air to escape when filling the tank that way. You can find any vent by just open the tank fill valve just a little and watch for water to run out.

My tank fill is pressurized, not gravity. you screw on the hose firmly then turn the valve to "tank fill" and fill it up.

 

[Rene T]

My tank fill is pressurized, not gravity. you screw on the hose firmly then turn the valve to "tank fill" and fill it up.

Yes I know. Many rv’s have both.
You can just open the fill valve maybe 1/4 of a turn allowing water to slowly fill the tank. Eventually you will see water running on the ground out from the vent.

 

[bigbAZ]

Here is what my fill port looks like, (I added the brass 90), the hose screws on and it is inside the wet bay. I suppose I'll have to park outside and top off the water and see where it comes out.

 

[Rene T]

I think you will have a vent someplace otherwise you could blow up the tank. Some campgrounds have pressures over 100 lbs

 

[bigbAZ]

Yes I don't doubt I have a vent, just curious where it is. I'm betting it's one of the 3 lines coming off the tank and probably ends up somewhere where it isn't exposed to much dirt and dust.

 

[CharlesinGA]

My Winnebago View had a similar valve setup and no gravity fill. The tank had a fitting on top that had an elbow, a piece of pipe, then another elbow, and a pipe running down thru the floor and was open just forward of the rear wheels. That was the tank overflow and vent, it had to stay open. There was a tap at the bottom with a valve and it also went out thru the floor, that was the tank drain. A line going in the top was the tank fill, and a line coming off a bottom was the supply to the pump. The tank sat on top of the floor under the stove, where the oven would usually be. It had a convection microwave above the stove. It was necessary to remove the bottom cabinet drawer to get to the drain valve. Previous owners destroyed the ball bearing slides on the drawers and I spent a couple of hundred dollars replacing them.

So yes, you need a open vent to allow air to exit when filling and air to enter when the pump is consuming water.

 

[CharlesinGA]

Just now realized you have a Winnebago product. Go to the WBO homepage and select OWNERS on the top right then on the far left is RESOURCES and you find Guides and Diagrams, operator manuals, etc.

Download all of this to a thumb drive and keep it. You never know when WBO might decide to dump all of this info into never-never land and it lost forever.

Your plumbing and waste drawings.

Your coach parts breakdowns. Not downloadable, rather interactive catalog.

Winnebago parts and accessories catalog, 2008, last one published, still useful to you.

Your wiring diagrams and install drawings. You need to download 16 different PDF files to get everything (some WBO wiring diagrams are consolidated in a "book" but yours are not.

2011 Via/Reyo H25Q Wiring Diagram Book​

110 Volt Load Center/Auto Transfer Switch
Antenna Installation, Radio and CB
Backup Monitor Installation
Battery Installation
Body, 110 Volt Wiring Diagram
Body, 110 Volt Wiring Installation
Body, 12 Volt Wiring Installation
Chassis Electrical Box Assembly
Chassis Wiring Installation
Dash Radio Installation
Exterior Lamps Wiring Installation
Front End Wiring Installation
Holding Tank Monitor Panel
Holding Tanks Wiring Diagram
TV Coax Wiring Diagram
TV/DVD Wiring Installation​

 

[CharlesinGA]

 

[bigbAZ]

That is some good info @CharlesinGA and I sincerely appreciate it! Will download all the files this week. Somehow I thought the interactive parts catalog was my only option for drawings.

I have a pro version of Adobe which will allow me to make the electrical drawings all into a single book again if I want.

 

[Kirk]

Yes I don't doubt I have a vent, just curious where it is. I'm betting it's one of the 3 lines coming off the tank and probably ends up somewhere where it isn't exposed to much dirt and dust.

Over the years I have owned several self-contained RVs and all of them had a vent line which also serves as an overflow. It does allow air to vent in or out as well as providing an overflow in case you forget to turn off the tank fill. Post #10 gives what you most likely have. I have never seen one with any kind of "flapper valve" as it must allow air into the tank as well as either air or water to exit. I have drunk water from all of the RV potable water tanks, and I sanitized the water systems annually. While I have not traced the vent line in all of them, but the diagram in post #10 is typical of the vent lines and I have never experienced any problem of contamination from them. The vent must exit outside of the RV because of the fact that it also serves as an overflow in case of overfilling to prevent pressurizing the tank, as the tanks are not designed to be pressurized and might fail if the vent line were to be blocked.

 

[Gary RV_Wizard]

Ditto what Kirk wrote. Yes the vent/overflow is open. Yes, some dust or airborne microbe (yeast, for example) could waft in. It won't kill you, but it's a good idea to have chlorinated water in the tank. If the fill source wasn't chlorinated, add a few drops or chlorine or peroxide.

 

[bigbAZ]

Ditto what Kirk wrote. Yes the vent/overflow is open. Yes, some dust or airborne microbe (yeast, for example) could waft in. It won't kill you, but it's a good idea to have chlorinated water in the tank. If the fill source wasn't chlorinated, add a few drops or chlorine or peroxide.

What I generally do at the start of the season is fill the tank to about 3/4 with water and bleach, let it sit for 24 hours, drain, and add back in my 10 gallons for travel. We always have hookups so I don't top it off, and we don't drink it. The tank is small at 27 gallons. Our city water is chlorinated as well.

 

[DonTom]

, but it's a good idea to have chlorinated water in the tank.

But the water filter removes the chorine, so how do you get the chorine in the water tank?

-Don- Auburn, CA

 

[NY_Dutch]

But the water filter removes the chorine, so how do you get the chorine in the water tank?

-Don- Auburn, CA

If your RV has a permanently installed filter with no bypass, just unscrew the canister, remove the filter element, and replace the canister to add the chlorine. You can even put the chlorine in the canister.

 

[bigbAZ]

But the water filter removes the chorine, so how do you get the chorine in the water tank?

-Don- Auburn, CA

Excellent point. At home I pour the bleach into the hose first then connect to my filter which is right at the spigot. However at a camp site when connected to their spigot I suppose the Camco filter I use will remove the chlorine, however I don't put that water in the tank, it bypasses the tank when we are hooked up.

There is one annual trip though, which happens to be next week, where I will need to top off my tank at KOA before going for 3 days without a water hookup. There's probably enough residual in the tank though from when I drained the bleach solution then refilled without flushing. And again, the closest we get to drinking tank water is brushing our teeth, everything else is bottled.

Now we do have a 3M filter under the galley sink which they don't make filters for anymore and I think I'm on my last filter. There may be an after market supplier for those.

 

[John From Detroit]

However at a camp site when connected to their spigot I suppose the Camco filter I use will remove the chlorine

I had one campground where my charcoal filter did not do the job.

But if I filled the onboard and let it sit a bit.> Well chlorine does not last long in a non-pressurized water container. Only in a solution like in a bottle of bleach. (there is a stabilizer in there)