Toilet to black tank seal-Issue resolved-Closing this post

[Frank C]

I did a search but didn’t find anything on this topic.   I’ve noticed a strong black tank odor when the bathroom exhaust fan is on, and the odor seems to be coming from where the toilet (standard flush toilet) meets the floor.  Seems that the exhaust fan is pulling odors up from the black tank somehow.   There’s water in the toilet bowl so I don’t think the odor is coming up from the black tank through the bowl itself.   I think there may be an issue with the seal between the toilet and black tank.  Before I pull the toilet up, for anyone who has taken out the toilet for maintenance, do you have any photos of the seal that is used between the toilet and the black tank?  Just so I have an idea of what to expect it should look like?   Is it a standard toilet flange and wax ring?
Thanks in advance. 

[SeaDawg]

If you're getting odors, you may have a venting issue. A birds nest, leaves,  etc, in the vent can cause odors to "back up." If your toilet holds clean water, even with the lid up, you probably shouldn't smell anything, imo, if venting is good and clear. 

In the meantime, close the lid after use. Pour just a little orange tank deodorizer in the bowl, along with the water,  after each use. The orange stuff from Walmart is cheap.

Rv toilet seals are not typically the same as home seals. It's  a pipe to pipe connection. Proper venting is important. As is a proper  clean valve seal within the toilet. 

We had an issue once in a rental delivery. I cleaned and  lubricated the bowl toilet  valve seal, and we were fine for the next 4000 miles.

[ScubaRx]

4 hours ago, FrankC said:

...Before I pull the toilet up, for anyone who has taken out the toilet for maintenance, do you have any photos of the seal that is used between the toilet and the black tank?  Just so I have an idea of what to expect it should look like?   Is it a standard toilet flange and wax ring?
Thanks in advance. 

Frank, I don't have any pictures but Lee Slusher and I swapped out Hull #050's original plastic toilet with a porcelain throne while out in Quartzsite a few years back.  It was a simple matter of disconnecting the water supply line, removing a couple of bolts and lifting the toilet out. There was no "seal" as in a wax ring, just a smaller pipe exiting the bottom of the toilet and going well into a slightly larger flange on top of the black tank. Also, there was no filth as I expected.

All that said, remember that the gray and black tank vents merge under the vanity and exit out the top of the trailer. If the outside vent exit is somehow blocked, theoretically sewer gases could back up and exit the shower drain. That's close enough to the toilet base to perhaps make the stink source confusing.

I once had mud daubers partially close up my vent pipe. I just took the cap off and put a water hose down inside it and flushed them all back down through the drains and into the waste tanks.

[Patriot]

Frank,

Have you checked and added water to the shower drain trap lately? We had a very slight odor emitting from the shower drain and I poured a few cups of water down the shower drain and the odor immediately went away. Our Ollie had been sitting with the dehumidifier on and I suspect it dried out the trap allowing an odor to escape up through the shower drain.  We always run the dehumidifier 24X7 so we periodically add water to the sink trap, shower trap, and galley sink trap. Might be worth a try.

 

 

 

[Geronimo John]

On 10/5/2021 at 3:11 AM, Patriot said:

Have you checked and added water to the shower drain trap lately? We had a very slight odor emitting from the shower drain and I poured a few cups of water down the shower drain and the odor immediately went away. Our Ollie had been sitting with the dehumidifier on and I suspect it dried out the trap allowing an odor to escape up through the shower drain.  We always run the dehumidifier 24X7 so we periodically add water to the sink trap, shower trap, and galley sink trap. Might be worth a try.

Very common for floor drains to go dry.  Try adding a table spoon of cooking oil in the P-trap (After winterizing of course with antifreeze).  The cooking oil will greatly reduce evaporation and when frozen totally eliminate it until spring!

[Frank C]

3 hours ago, Geronimo John said:

Very common for floor drains to go dry.  Try adding a table spoon of cooking oil in the P-trap (After winterizing of course with antifreeze).  The cooking oil will greatly reduce evaporation and when frozen totally eliminate it until spring!

I had done all that usual checking of the traps, etc.  The issue actually turned out to be a broken & cracked toilet mounting flange (see photos) that allowed black water to leak under the toilet and drip down onto the top of the black tank and between the hulls, causing the odor issue.   The crack grew progressively worse over time and eventually the source of the problem became very apparent as water leaking out of the under-hull scupper below the bathroom anytime the toilet was flushed.

Oliver uses an all plastic toilet flange which is common in residential applications but seems prone to cracking with a heavy porcelain bowl toilet in a trailer bouncing down the road.   Other owners have discovered this same problem (sometimes on a brand new trailer, seems the flange occasionally gets broken during installation of the toilet).

 I replaced it with a new toilet flange that has a stainless steel ring for holding the toilet mounting bolts.  I also installed a new Dometic seal between the toilet and flange.  Problem solved, odor gone (after some cleanup & disinfection between the hulls around the black tank).  Thankfully we only ever use the toilet for #1.   #2 is done at the campground restrooms or roadside rest stops.   Made cleanup a lot less of an issue. 

[Geronimo John]

Pstar post thread 20 APR 2020 came to the same conclusion.  Thanks for the reminder to all of us!

 

 

GJ