Teardrops n Tiny Travel Trailers

I just assumed that the fresh water tank vented through the fill tube, but I got my gravity fill inlet today and it has 3/8'' barb for a vent. Do I need a seperate vent if the fill tube goes to the top of the holding tank?

I would. The instructions that came with mine said to. It will definitely make the water flow easier, for filling, draining, and sink usage. Here's a picture of how I did mine. (Because I am using such a small space and the hose tended to crimp, I used CPVC elbow connections at the bends, glued with CPVC pipe glue. I used screw connectors on all but the air vent. It has the round black squeeze ring on it. The drain tube is mounted on the back end of the tank but you can't see it in this picture. There is a picture of that in my album.)

Yes, you need to connect a separate tube from a port near the top of your tank, and connect it to the barbed fitting on the gravity fill.

Without a separate vent, the water pump can collapse your tank.

Rob

Rob, no offence, but I would love to see a diaphram pump collaps a 6'' schedual 80 PVC pipe. All jokes aside, the tank won't pull in air through the fill tube?

DH,

None taken!

I don't know about a schedule 80 PVC tank, but in another camper I built, I once forgot to open the vent tube (I had a shutoff on it for travel and storage) the pump sounded like it was laboring, so I checked the RV fresh water tank, and found it quite distorted!..
I did have a sealed fresh water fill port, which contributed to the collapse...

When you fill your fresh water tank, the fill tube will be full of water.
The air in the tank will have no where to go.
Having a separate vent will allow the tank to fill much faster without burping and spitting water back out the fill tube.
You can fill without a vent, but it must be done very slowly.
It may be overkill, but I prefer to have fresher air from inside the trailer be drawn into the tank to replace the water, than whatever might be in the air outside the trailer (dust, bug spray, smoke, etc.)

It is possible over time, for your fill tube to be crushed or deteriorate allowing the pump to pull it completely closed, again threatening the tank.

Rob

That makes sence. I always had a problem with how open the fill ports on the holding tanks were on the older campers, I don't know if venting inside the camper would work in my build, but what about usind a fuel filter in line to filter out whatever gets drawn into the vent from the outside?

A filter of some sort (a bit of sponge or scotchbright pad) might help keep bugs and such out of the tank. I guess if you wanted to get carried away with the idea you could use a respirator filter to clean the air that must enter the tank as the water level drops. I have never used one though.

If the filler neck is short and straight enough that you can get the end of the hose down to the tank itself a separate vent would not be necessary for filling the tank but there will have to be some way for air (or water) to enter the tank as the water level falls, or exit as the water level rises. A separate protected vent and a secure sealed water inlet seems like a big step toward keeping the water in the tank fresh and clean.

A vent is a definite must. I watched a 2500 gallon steel diesel tank crush itself because the vent didn't get opened and it was simply gravity feeding into an underground tank through a 4" hose about 6' long. Air pressure has a funny way of being a whole lot of force. At 14 psi (sea level air pressure) a 12" x 12" side of a water tank would have to withstand over a ton of crushing force. A 40 psi water pump has the capability of producing almost 3 times that much force.

An extreme example...

Corwin,

That is a cool video!

Though I know different, the tanker looks no stronger than an aluminum can...

Rob

I can see the value of a vent line though and I am thinking running it to something on the frame for a filter as my fresh water tank is mounted under the flour of my teardrop and is like a gas tank mounted underneath the frame.

if bugs and dirt are going up your vent line into your water tank they do make a non expensive in line filter that goes in between your faucet and the fresh water tank like if you have a electric pump it would go between that and the sink faucet.

Mr. Cowboy,

A vent terminating just above your tank will help, but you will likely be much better off to have it a couple feet above the top of the tank.
A vent lower than that will allow water to slosh out.
A vent opening under the trailer would also invite road spray during a rainstorm, and anything else that is kicked up on a dusty road to make its way into your tank.

A filter is a good idea, but it is generally much preferred, and safer, to be sure only safe water gets into your tank to start with, via the fill port or vent, as once contaminants enter the tank, the tank itself is no longer "safe" for water storage, and bugs and junk can foul the pump and faucets/aerators.
Yes you can sanitize the tank, and no, a few bugs won't hurt you, but most folks would rather have clear clean water...
A filter on the incoming end of the air vent would be the easiest way to avoid problems.
I have a double layer of copper screen wire, and a piece of cotton cloth on mine, which is inside the trailer, to prevent bugs and dust from entering.
I guess I could get more serious and hook up some super filter, but bugs and dust are my only concerns.

Rob

Same here, just concerned about bugs and dust, figured a simple in line gas filter would be easy and cheap, just have to find one with 3/8" barbs.

Doh, forgot to mention, I took the filler out of the package today, the filler port cap has a gasket in it, so ya, I gotta have a vent.

So, I'm pretty new here, and really new to plumbing, but from what it seems, wouldn't there be an issue of water coming out of the vent opening if your tank becomes too full? How would you control that?

So, I'm pretty new here, and really new to plumbing, but from what it seems, wouldn't there be an issue of water coming out of the vent opening if your tank becomes too full? How would you control that?

Hi Ashley,

Most systems are designed with the vent higher than the fill.
When filling the tank with water, any excess spills back out the fill port, before the hose is removed.
After filling the tank and capping the fill port, if the vent tube terminates a foot or more above the top of the tank, the water loss is minimal.
Most fill ports have the vent tube terminating in/next to the fill port area, so any spillage is outside.
The loss is generally very small, just a few drops.

Rob

Rob,
Thanks for the reply- that would make sense. I guess my only other question would be what if you had a check-valve in place on your fill side?