Black Tank Odors

[jpmyers]

I dump and backwash my black tank weekly. I run backwash cycles of 5 minuites with the dump valve closed to allow clean water levels to rise during the backwash.

After having clear water coming from the tank from two consecutive flushes, I'll close the dump valve and run the backwash for 15 - 20 seconds and leave that in the tank to mix with the tank chemical I put in every week.

My issue is that in the past month or so, the odor from the black tank has become really bad. I have gone in from the top side with an angled wand to clean what I can from there. After doing this weekly for 2 years, am I somehow missing a step? Or is there something additional/different I should be doing after two years of use?

[mordecai81]

We had a similar issue last year with our 4 year old TT. I sniffed around and the stink seemed to be coming from the toilet pedestal. Upon removing the toilet I found that the foam seal that seats into the floor flange had compressed and was not sealing properly. Replaced the foam seal/gasket and took the opportunity to give the nooks and crannies of the whole throne a thorough cleaning. Took care of the problem. I plan on preemptively replacing that seal every few years.

[opnspaces]

Home Depot website seems to call the AAV a cheater vent.
Link

[ken56]

I agree with the air admittance valve for the sink/grey tank. Been there done that.

[Pangaea_Ron]

I abandoned the check valve and ran flexible tubing from the removed check valve pipe to the exterior.

Life is good now!

[Pangaea_Ron]

MFL might have identified your problem.

My grey water vent pipe was installed too deep into the tank and would not function when the tank became full, and would vent through the kitchen sink.

[BurbMan]

Ditto on the AAVs, there is probably one in the kitchen and in the bath, replace both. Also, more fiber in your diet can alleviate odors as well.... 🙂

[IAMICHABOD]

As others have said, I would check and replace the air admittance valves
located near your sinks,they are cheap and can be found at most big box stores like Home Depot and Lowes as well as smaller hardware stores.

If they fail they will let the smell from the grey tanks in and believe me they can smell just as bad as the black tank if not worse.

Changed mine out and the smell was gone!

They are used to keep 'P' traps on sinks from getting sucked dry when draining grey tanks.

They are downstream of sink 'P' traps on a short stub pipe.

[RoyF]

wildtoad wrote:
Is your backwash a process where you attach a hose to the end cap? Or is it a black tank flush connection? If the latter there is a back flow preventer typically under a bathroom sink than can go bad and allow fumes to enter the bath.

I would like to learn about this backflow preventer. I have always wondered about a water line under my bathroom sink that is capped off and seems to serve no purpose. I suspect that it connects to the black tank because it comes up from below. (The underbelly is enclosed so I can't see where it actually goes.)

[wildtoad]

Is your backwash a process where you attach a hose to the end cap? Or is it a black tank flush connection? If the latter there is a back flow preventer typically under a bathroom sink than can go bad and allow fumes to enter the bath.

Where is your black tank vent in relation to any open roof vent? In my case the vent pipe is directly behind the bathroom vent depending on wind fumes may enter the RV.

[Lwiddis]

Are you stationary or mostly stationary? Try filling 2/3 full, adding dish soap liberally and taking a start/stop, lots of turns, ten mile drive and then dumping.

[MFL]

Have you checked to be sure black tank vent on roof is not plugged, or dropped to bottom of tank?

Gray water tank can smell just as bad, and if under sink air admittance valve needs replacing can make a big stink.

Jerry

[jdc1]

Where is this smell coming from? It is a closed system. The only opening is a vent, up on the roof. If you are expecting the tank to smell like roses, give it up, it'll nebver happen. Those chemicals? Waste of money. Just add liquid dish soap once in a while.