obnoxious sewer gas with each flush

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obnoxious sewer gas with each flush - Not For Us

July 05, 2015, 07:51:49 pm

Mary et al.: We run the vent in the bathroom whenever we need to. Flushing odors are not a problem in our RV with vents running. We do not use commercial chemicals in the toilet.

We only use dish detergent, like one-half to one cup of Dawn, and a generous sprinkle of Borax powder. We put some clean water in the tank after dumping, add the Dawn and Borax. Periodically, we add one or both between dumps. We also occasionally use a couple of tablespoons of toilet seal preserver in the toilet bowl with the usual water. We only hook up to dump when we need to dump. We never stay connected to the park's sewer system.

We once had your problems (both while on the road and when sitting in place) in our 2004 $400K RV that we bought in 2006. It was BAD. We installed the cyclone toppers, etc. We had the tanks steam cleaned. Nothing worked until we moved away from commercial chemicals and began following the practices mentioned above, which provide continuous cleaning of the tanks.

If there is still a problem, it will be structural or mechanical and you might need help with that. An example of this is a surprisingly common problem with RV vent systems--the vent pipe is too low and cannot vent because it sits IN the sewage rather than above it.... You will notice this odor when driving down the road.

Terry Apple

Full and part-time RVing since 1974
2013 27RB

Re: obnoxious sewer gas with each flush - Not For Us

Reply #1 – August 19, 2016, 08:44:42 pm

Here's another possible reason for sewer smell in the bathroom: a poorly sealed opening where the toilet pipe enters the floor on its way to the black tank.

I'd recently had an increasingly noticeable sewer smell in both the bathroom and the cabinet under the kitchen sink of my 2003 midbath. (The kitchen sink cabinet has a sizable opening into the bathroom, with the gray water drain pipe heading aft through it.) Turning on the bathroom exhaust fan made it worse. And the smell was much worse as the black tank reached 100% full (per my SeeLevel gauges).

But this wasn't the usual case of the toilet burping bad odors when the tank was full; in fact, I wasn't even using the toilet. It smelled bad all the time. Yet the toilet's seal was in good shape (only a year old) and was holding water. And there are no vents around the rim, unlike some older toilets.

After a lot of nosing round, culminating in cutting a sizable opening in my bathroom floor to gain access to the pipes under the toilet, I discovered the cause: there's an oversized opening in the subfloor about eight inches forward of the toilet, where the sewer pipe takes a 45° turn downward to meet the black tank's inlet. That hole was partially filled with cheap expanding urea foam--the same yellowish stuff that was unfortunately sprayed all over the undersides of my tanks--but there was a gap on the aft side of the pipe that I could easily shove my finger through. That gap led right to the top of the black tank.

It's a safe guess that the donut sealing the pipe to the tank is leaking just enough to let some smell out when the tank is full, even though crawling under the rig, I found absolutely no sign of fluid leakage. And with the partially unsealed gap around the toilet pipe, evil odors are easily sucked up into the rig, seeping into both the bathroom and kitchen. The solution, which I'll implement in the next couple of days, will be to put a collar of galvanized flashing around the pipe, effectively sealing the opening and preventing smells from coming up through the floor.

In the long run, I'll probably have the black tank dropped and that donut replaced, so the tank top is sealed as well. (Dropping the tank should also allow sealing off the hole in the subfloor from below, but I'm not equipped to do that, and the nearest RV repair place is quite a few miles away.)

For your amusement, here are a couple of photos of things you don't normally get to see. The first, looking rearward and upward to the underside of the raised toilet platform, shows the pipe exiting the toilet. The foil-covered area underneath the pipe is the top of the left rear wheel well.

The second photo, looking straight down with the outside of the coach at the top of the image, shows the pipe entering the subfloor. Unfortunately, the photo only shows the part of the opening that is filled with foam; you can't see that the whole aft side of the opening, hidden under the pipe, has no foam at all. That's where the smell gets in.

(By the way, you can see the sharp angles at both ends of this short run; that's why the midbath's toilet is so prone to clogs.)

Re: obnoxious sewer gas with each flush - Not For Us

Reply #2 – February 21, 2019, 04:49:34 pm

Here's an update on that sewer smell issue I had three years ago. Much later, I learned that my diagnosis (as explained in the previous message) had been completely wrong. Yeah, it wasn't a good thing that the pipe coming out of the toilet was not sealed where it passed through the floor on its way to the black tank. But that wasn't what was causing the smell. The problem was entirely of my own making.

When I bought Skylark back in 2006, one of the first things I did was to install a SeeLevel II tank gauge system. In the process, I did something I thought was clever: in order to hide the wires running from beneath the kitchen floor to the upper cabinet where the gauge panel was installed, I ran them inside the black tank's vent pipe, which was conveniently located in a corner of the kitchen. Of course I sealed the holes where the wires entered and exited the pipe... but that sealant had loosened up over the years.

In short, the bad smell was coming from poorly sealed holes I had drilled in the black tank's vent pipe under the sink. It was a stupid thing to have done; I could have just run the wires up the back outside of the pipe and they would have been just as invisible. Worse than that, I wasn't even the one who figured it out and fixed it. A friend of mine who was helping me spruce up Skylark before handing it over to its new owners figured it out, and went through painful contortions to get under the sink and reroute those wires.

Mea culpa. Mea maxima culpa. It was all my fault.

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July 05, 2015, 07:51:49 pm

Reply #1 – August 19, 2016, 08:44:42 pm

Reply #2 – February 21, 2019, 04:49:34 pm

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