Gray tank smells

[Pangaea_Ron]

I've posted about my problem before, and here is what I think is happening.

The gray water vent was installed low into the gray water tank, and did not project through the roof. I have corrected the issue as it projects through the roof plane and have installed a rotating venturi vent, which helps.

I have tried pulling the thru roof vent line upwards (as others have suggested), but it is restrained by a lateral shower drain, and cannot be raised.

When the tank fills (about 2/3 full), the bottom of the vent is submerged below the water level in the tank, and gases find another way to escape, and that is usually through the kitchen sink drains. If I close the drains, and fill the sinks with a bit of water, the smells do not occur. The "P" trap below the sinks does not seem adequate to prevent the smells. I have replaced the under-counter vent frequently.

I am considering putting a "T" in the vertical line to the under-counter vent and running a vent line downwards through the floor level to the exterior below the chassis. It's not a perfect solution. but running a vent line to the exterior is not possible through the roof or wall. It seems like the gasses should follow that route rather than upwards through the sink drains.

Dropping the tank to investigate seems like a formidable task.

Any thoughts?

[Pangaea_Ron]

Oldme

That's a good thought. At home I regularly add water to P-traps of un-used plumbing fixtures to avoid smells passing through dry P-traps.

Unfortunately dry P-traps are not my issue, the build up of pressure (or sloshing) can overwhelm water in the P-traps, when the roof vent is blocked.

[Oldme]

If your P-traps dry out from evaporation,
the lack of water in them will allow
gas/odor to pass.

[Pangaea_Ron]

I took a plumber friend to lunch yesterday and he suggested something to try.

He said to remove the threaded under-counter vent and replace it with threaded reducing bushings until I can get a 3/4" bayonet hose fitting to fit. Then attach a 3/4" hose that extends to the exterior.

It should allow gray tank smells to get to the exterior, and would also prevent a vacuum from forming while draining the kitchen sink(s).

This seems like the easiest approach, which I will try this weekend.

[BarneyS]

Seems to me you would need to make a longer/deeper P trap and not just lower the thing. The water level would stay the same in your idea, unless I have the wrong picture in my mind. Just lowering the whole thing down from where it is now will not do a thing except give you a longer drain to clean stuff out of. Water always seeks it's own level.
Barney

[Pangaea_Ron]

I think that my first approach to the problem will be to drop the existing "P" trap for the kitchen sinks to create a more formidable barrier to air escaping from the gray water tank. I can lower the "P" trap about 12" that would create more than 24" of water column for the offending air from the gray water tank to penetrate.

Any thoughts about this approach as a first step?

[Pangaea_Ron]

Thanks for all the input!

I'll climb around this week and see what is possible. Unfortunately the existing vent through the roof is about 10 feet from the offending sinks with no reasonable way to access it. The under-counter vent is located high within the sink cabinet and has room to easily add a "T" fitting that would not be prone to allowing water access from the tank.

It's interesting that the shower does not emit any odors, only the kitchen sinks? The shower seems to drain into the common drain/vent pipe that goes through the roof. The Plumbing Schematic available from Winnebago, although helpful, is not the same as for my installation?

I use the GEO system in both tanks and am not a fan of using other treatments to cover (or eliminate) the smell. The issue seems to be pressure build-up through adding water to the tank, or sloshing within the tank while driving (most frequently) and overwhelming the "P" trap.

Thanks again.

[sdianel_-acct_c]

We put 1 cup of Dawn Platinum and 1 cup of Borax in our grey tank after we dump and about a gallon of water, and now no odors!

[YC_1]

Ditto Bobbo: You can use a rubber coupling with two clamps. They are available at any Lowes or Home Depot. Mine had the same problem. To seal the bottom again there is a great product available at the same places. Goop. Goop is available in several flavors but any will do the trick. It comes in Plumbing, Marine, etc. I think it is the same stuff. It is very sticky and you will spend a couple of days peeling it off your fingers if you don't use gloves.

[Bobbo]

The real solution is to fix the problem with the gray tank vent. You need to get a vent from the gray tank, high enough to be above the fluid, out through the roof.

I can see a couple of ways.

1. Drill another hole in the top of the gray tank and install another vent line making sure the bottom is high enough. Put an elbow in it and "T" into the current vent line so it goes through the roof.

2. Cut the existing vent line BELOW where its "T" goes to the sink. Pull the vent out of the tank and cut it off so it only sticks a couple of inches into the tank. Re-insert it into the tank and use a coupling to tie back to the remaining vent line.

Do it right, and you do it once. Be sure that you get a good seal around the vent where it enters the gray tank with either of these two repairs.

Anything else still leaves you with a pressurized tank when it starts filling. If you have a pressurized tank, you WILL have problems no matter how you try to patch it.

[GENECOP]

If you have ever had a foul smell in your RV and couldn’t figure out where it was coming from, we may have the answer for you.

All RVs with holding tanks have a vent pipe secured in the top of the holding tank and going up through the roof, which is where the odor created in the tank is vented. In addition there are the tank inputs coming from the sinks and toilet as well as the shower. To prevent odors from coming into the coach from these devices, other products had to be installed inline, the most common used in the sink and shower drains is the P-trap.

P-trap.

A P-trap uses water in the bottom of it to isolate the coach air from the tank air. You may also have an anti-siphon trap vent device (ASTVD) under the sinks. It is a small ABS plastic device fitting found near the P-traps under the sink. Its purpose is to allow air into the P-traps under that sink, and at the same time prevents sewer gases and odors from coming in from the holding tank and main piping.

ASTVD Vent

A typical roof vent prevents water from entering the tank from the vent and in addition creates a venturi action as air passes through the vent cap.

There are a variety of different designs for P-traps, ASTVD devices and roof vents, yours may look different from the photos but they all work in principle, the same.

The issue we explore in this blog is the P-trap itself as it relates to RVs.

As shown in the photo above the water in the trap is the isolater between the inside of the holding tank and the inside of the RV. Gases do not leak through water and as a result, it is a simple method currently used almost everywhere. The issue with water P-traps in RVs in particular is the fact that the RV moves and can displace the water breaking the isolation barrier, allowing the gases to come into the living space of the RV.  Another issue is the amount of space a typical P-trap takes up, especially under the shower drain. A lot of RV manufacturers are now using a new device called HepvO, to solve the space issue.

 

          

                                 The HepvO is a waterless trap!

 

The HepvO allows water to flow through it, but does not allow it OR sewer gases to go the other way. Simply put, it is a “check valve” of sorts. The product is not a lot bigger than the drain pipe itself , approximatly 7 1/2? long by 2 7/16? in diameter maximum. In most cases the standard P-trap can be replaced with the HepvO which comes in two sizes 1 1/4? and 1 1/2?. The size you would need is determined by the sink down pipe size. The kits come with the most common fittings needed. Addditional fittings, adaptors etc. if needed, can be obtained at a local hardware or plumbing store.

The HepvO valve has been used in most other countries world wide in housing as well as commercial buildings and will be in North America in the future, after plumbing code approval. The product is listed currently and a building inspector can approve its use. The RV Industry’s RVIA has approved its use in RVs.

For more information go to www.hepvo.com or call us 877 787-8833 toll free.

Just found it....

[GENECOP]

I have seen a new option, can't remember where, but it replaces the P Trap with a self closing kind of sleeve....it can be mounted Horizontally or Vertically, and had great reviews, I think It would solve your problem....search around, if you can't find it post back and I will hunt around....

[Old-Biscuit]

Your issue is 'physical' in that the vent line gets blocked by level in tank.....chemicals/foo-foo odorants won't resolve your problem

When vent gets blocked off pressure builds every time you put more water in (sink/shower etc.) as water is heavier than air so the air has to get pushed out.

The air admittance valves are designed to CLOSE under pressure (unless worn out and don't seal) so the air gets pushed up thru 'P' trap.

Tying into the vent line portion (not drain line section) will allow air to escape tank as water drains into it....even if it goes downward and out thru floor.
Not the most ideal corrective or conventional measure.....but easier than dropping tank, pulling vent line and cutting it off then reinstalling vent line/tank PITA!!!

Is there enough room on vertical section of stub pipe where air admittance valve is installed to cut and put a 't' in???

Mine stub pipe is very short

[TucsonJim]

Ours was pretty stinky, so we tried some of this stuff:

TST Gray Water Treatment

No more stink. Before you go to a whole lot of labor, you might try using some of this odor controller first.

[navegator]

Can you run a vent line from the area of the Ptrap to the vent tube, son that the gas travels up to the T fiting before the P trap and onto the vent tune?

navegator