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Old 07-31-2015, 06:08 AM   #1
Join Date: Oct 2012
Location: Denton, Texas
Posts: 96
Black Tank Odor

Over the past few months we've started experiencing toilet odor after 4 days or so accumulation in the black tanks (we have two separate black tanks). Both tanks have the same problem.

We empty tanks once a week and flush the tanks each time before treatment. We've tried different off the shelf treatments and added qty of treatment above the recommended amount (e.g., 3 or 4 tabs vs 1). We have also increased the amount of water added to the tank throughout the week.

Any suggestions on how to stop this?

Read another post talking about a black tank vent? Is that true? RV black tanks have vents? Appreciate the help.


Gary and Karen Allison
Denton, Texas
Redwood 39MB, Lance 1181, Ford F-350 Diesel, 4X4 Dually
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Old 07-31-2015, 07:26 AM   #2
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This can be a tough problem in RV's. We had the problem a lot when ours was new and now we only have it once in a while. It happens most when on the move rather than stopped. It is worse when it is hot. Ask 100 different people and you will get 50 answers. Here are the things we have done.

Treatments- We haven't noticed much difference between them. Our technique is to first of all add the proper amount of stuff after we dump and then make sure we put perhaps 2 gallons of water in the tanks. If it is over 80f and we are moving we will add another dose every couple of days while moving. Every day if over 90f and moving. Either way try to get the treatment in there before using it.

Vents- We tried the ones that turn with the wind and then we tried the one with the fan. The one with the fan helps somewhat but we only use it when it is stinky. I can't say that it is all that effective but it does help somewhat.

The toilet itself- There is usually a trap on the fill line that has water in it. It can run dry when not used. The rubber ring between the toilet and the pipe can go bad and need replacement. You need to unbolt the toilet to check it, bu the time you do that you might as well replace it. Don't forget to disconnect the water first. Make sure that there is some water staying in the toilet between uses. The rubber gasket can wear and leak fumes if it is old. If you are opening the hatch when driving it can suck the fumes up from the tank. This next one is sort of a tinfoil hat opinion. I decided that the plastic toilet might be allowing smells to come up through the plastic like a cheap fridge container that lets smells get in the food. I painted mine. I was tired of the old fashioned almond color anyway. I could be nuts. I think it helped a lot. You need to be really care full and sand everything so the paint sticks.

Those are the things that helped us. I'd start with the easiest ones first. Good luck and happy motoring.

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Old 07-31-2015, 09:21 AM   #3
Join Date: Oct 2012
Location: Denton, Texas
Posts: 96
I just spoke to the service desk at my dealer. He's checking with their tech's, but said we may want to put bleach in the tank. I asked him to verify that would not eat any seals in the tank which we would obviously need. Anyone try this?
Gary and Karen Allison
Denton, Texas
Redwood 39MB, Lance 1181, Ford F-350 Diesel, 4X4 Dually
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Old 07-31-2015, 09:26 AM   #4
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Don't turn on the exhaust fan while flushing the toilet. The negative air pressure can draw the smell inside the coach this way.

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Old 07-31-2015, 09:34 AM   #5
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Thanks, but we're aware of the exhaust fan issue and don't do that. We also aren't traveling, which would make it worse. I'm going to climb up on the roof and make sure the vents are clear later today.
Gary and Karen Allison
Denton, Texas
Redwood 39MB, Lance 1181, Ford F-350 Diesel, 4X4 Dually
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Old 07-31-2015, 10:09 AM   #6
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Periodically we'll toss one of those dishwasher detergent pellets into the tank along with a few gallons of water before a driving day. Seems to loosen residue and even got the sensor back to working. Don't think I would use bleach.
Dave & Jo Ann
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Old 08-04-2015, 05:57 AM   #7
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To start with I always dump the black tank when it's full. When getting ready to leave a camp site I dump all tanks. If the black tank isn't full I fill it with water via the tank rinse before dumping. Dump the black refill and dump again. Let the tank rinse run till the gray tanks are empty, close the drain valve and leave the rinse on a few minutes to add water to the black tank. I put a 1/2 cup of "liquid water softener", 1/2 cup of bleach and 1/2 cup of pine sol to the black tank and drive to the next camp site. I don't empty the tank again till it's full. All the sloshing while traveling gives the black tank a good scrub, the water softener keeps things from sticking to the tank and sensors. When we are at a site for an extended stay and need to dump tanks I always add water after dumping and use the bleach and pine sol. Only use the "water softener" NOT fabric softener after every third dump. I do use laundry detergent in place of the pine sol at times, both work good. This is my third RV doing things this way. Never an odor, never a problem.
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Old 08-04-2015, 06:01 PM   #8
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I've read a post similar on black tank odor and the solution PhoneDude gave is spot on. It's a good solution for black tank odor, the blue tablets or liquids do not work, and I'm not a fan of that odor either. If your in West Texas or parts of NM the Potable Water can have a bad odor, rotten eggs, sulfur. You will only use the water once in Fort Stockton!
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Old 08-05-2015, 06:42 AM   #9
Join Date: Oct 2012
Location: Denton, Texas
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Thanks Phonedude for such a detailed response. Thanks to everyone for their thoughts and recommendations. We'll give these ideas a shot at fixing the problem. I can breather better already!

Gary and Karen
Gary and Karen Allison
Denton, Texas
Redwood 39MB, Lance 1181, Ford F-350 Diesel, 4X4 Dually
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Old 08-05-2015, 07:08 AM   #10
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Phonedudes method is spot on! Good video depicting the process is on RV Geeks. I have followed it faithfully and not had a problem!

How To Dump & Clean An RV Black Tank - TheRVgeeks

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odor, tank

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