Black Tank Odor

[sdunn4]

We have a 2015 Roadtrek SS Agile and have put 10,000 miles per year on it as an average. Today for the first time we smelled a sulfurous odor from our back tank / toilet. The smell came on suddenly while driving today around northern VT (about 75 degrees and good roads). We’ve never used it for # 2’s; just #1’s. We flush and drain each trip and use the toilet deodorizing fluid regularly. I thought maybe our vent pipe was plugged so managed to climb up and look but couldn’t find a vent from the roof. Anybody have a similar issue and how did you resolve it? Any info on our model venting / P-trap setup would help as well. We added a couple gallons of water to the black tank and will dump when we head home tomorrow. Each time we flush there’s quite an odor And then it persists so we are leaving the restroom fan running overnight. I’m also making sure the shower drain P-trap is full and screwed the drain plug in to rule that out (added the deodorizing fluid into that drain and the sink drain just to also rule out the grey water tank).

Thanks, Steve

[rowiebowie]

Sometimes gray water can generate quite an odor. Have you tried pouring water down sink and bath drains to make sure there is water in the p traps?

[themexicandoctor]

Rowiebowie is correct - Gray water when it comes into contact with food particles & micro amounts of skin & anal secretions washed off in showering can be pungent.

9 years of ownership & I have learnt what each tank smells like.

Sometimes a tablespoon of bleach is all you need in the sink & into the ptrap & then flushed with in a day*.

*the bleach is bad for the seals

Could your ptrap be leaking?

Sometimes in a black & gray tank, where there is no oxygen & driving in hot weather that heat is transferred into the tanks causing the smells to multiply in potency.

[mkguitar]

there has to be a vent somewhere...

creating a "low pressure" in the van by using an exhaust fan or driving with windows down can pull gasses from the tanks into the cabin
is your vent fan reversible?

on my van with a vent stack thru the roof I added a Lippert 360 venturi to pull air out the stack

like you we don't use our toilet for solids. and we don;t use much in the way of chemicals.
even so once in a while there is funk in there remediated by dumping and flushing

I do carry powdered DiChlor ( pool shock) which is what I use to sanitize disinfect the fresh water tank prevoyage- and I have used that in the tanks ( 1 tablespoon max) with water overnight, then flushed

my shower pan fitting in the floor required a wrap of teflon tape to get a good seal


some of the "hippie" grooming products use organics which can feed growth ...like dr bronners and others which use food grade type oils and scent agents- trying any new products?


mike

[avanti]

Originally Posted by mkguitar

creating a "low pressure" in the van by using an exhaust fan or driving with windows down can pull gasses from the tanks into the cabin

This is true, but only if there is a leak somewhere in your plumbing system. Unless there is enough pressure to bubble gas up through a trap (which is not impossible, but you would surely know it), a properly operating RV sewage system is just as well-sealed as is the one in your home, and you should no more expect your head to smell than your home bathroom. (The exception to this when you actually have your foot on flush pedal--you CAN get smell during that brief period.)

A negative-pressure device for your vent stack can help, but it is a palliative fix. Better to find and repair the real problem.

[sdunn4]

Thanks for the great ideas and comments! An update:
- once we dumped the black tank the smell was gone immediately. We had really filled the tank with extra water and while using the macerator pump I sensed a “heavy flow” in the dump line (it pulsed quite a lot). Maybe there was a buildup of some RV toilet paper? That’s all that goes in except pee and water....
- possibly we had a plugged vent? By dumping perhaps a vacuum was drawn enough to clear the vent?
- more importantly, do any of you that own the Roadtrek SS Agile know where the black and grey tanks vent? We have 3 solar panels on the roof and perhaps they cover the vent? There are no apparent vents on the roof; I have never seen one in our 5 years of ownership and multiple washings I have given the roof and solar panels.

Thanks again for taking time to read and reply; this forum is a great resource with lots of folks generous with their time.

Steve

[arvitrekking]

We also have an SS agile. We have found that if we don’t completely flush and rinse the tanks several times every couple months that we get the odor that you described. I fill the tank about 3/4 full and add some dish soap. Then drive around a little to slosh it around. Then completely fill and drain three times or four times.

[sdunn4]

Thanks Avritrekking,

Great ideas you have mentioned; we’ll try those steps as well. Have you figured out where the black and grey tanks vent from the vehicle?

Thanks,

Steve

[David Pouliot]

Sometimes if you do not push the gray and black valves they cross contamanate
Conferm the vent pipe is not blocked on the roof ..they make a vent cover that promotes exaust though a vortex
In any case use fabric softener in each tank ..put a bag of ice in the black tank though the toilet and go for a bumpy drive
.this makes all oders go away and keeps things from sticking to the tanks

[OregonTrader]

We also have a 2015 Agile, and we also get the black tank odor occasionally, but only while driving.

Keeping the tanks clean helps a lot. But really, it should be a sealed system and you should not be able to smell anything.


The vent is under the solar panel on the passenger side. It vents both tanks. I suspect this the odor is caused by a downdraft from the vent, but am not sure. I'm considering adding some kind of venturi contraption on the vent outlet, if I can find one that will fit under the solar panel. Not much room there.

Enjoy your Agile!

[sdunn4]

Thanks for the pertinent information! I will try the fabric softener / ice cubes as that seems like a great idea. Also thanks for the information on the vent location; I will get a good look to make sure I know where it is (we have 3 solar panels and I’m pretty sure the vent will go straight up from the toilet location).

Thanks,

Steve

[themexicandoctor]

No, something bigger is happening there and or, the vent is damaged or blocked.

You only need a small amount of fecal bacteria to colonise a tank & begin the fermenting process.

Everyone seems to be doing superhuman efforts. The are not fun or easy.

I have filled, emptied, flushed & filled my tank sometimes right to the top for 9 years every 10 days - the only time when I noticed a serious odor was when driving a 1000 miles over 2 days & the heat from the exhaust & drive train being transferred into the tanks.

Some photos would help.

Let's find this vent for these guys.

[themexicandoctor]

It could simply be a leaking ptrap.

[sdunn4]

I located the vent this morning; it’s under the rear passenger side of the middle solar panel. There’s only ~1/2” clearance to the underside of the solar panel. We “may” have lodged some leaves above the vent pipe and covered the vent when navigating into our campsite in northern VT a couple weeks ago- that would explain our odor!

I’m attaching a photo taken from the rear of the solar panel.

Thanks again for taking the time to help!

Steve

[booster]

Originally Posted by sdunn4

I located the vent this morning; it’s under the rear passenger side of the middle solar panel. There’s only ~1/2” clearance to the underside of the solar panel. We “may” have lodged some leaves above the vent pipe and covered the vent when navigating into our campsite in northern VT a couple weeks ago- that would explain our odor!

I’m attaching a photo taken from the rear of the solar panel.

Thanks again for taking the time to help!

Steve

That area might be turning into a high pressure area at driving speeds and forcing a reverse flow of air in the system.

[mkguitar]

if you dont have clearance for a venturi type cover


you could add a 1/2 round pipe of pipe to the front of the vent extending up almost to the underside of the panel


like a cupped hand, this would cause a low pressure on the backside and pull air up the vent while driving


the venturi covers sold are intended to work driving or parked no matter the wind direction



mike

[GeorgeRa]

I found my borescope to be a very useful tool to see places not easily accessible. I bought it a good few years ago, used it not too often but every time it saved me a lot of time.

https://www.amazon.com/DEPSTECH-Wate...RQSMYK2632JP8E

[booster]

Originally Posted by mkguitar

if you dont have clearance for a venturi type cover


you could add a 1/2 round pipe of pipe to the front of the vent extending up almost to the underside of the panel


like a cupped hand, this would cause a low pressure on the backside and pull air up the vent while driving


the venturi covers sold are intended to work driving or parked no matter the wind direction



mike

I was thinking the same thing about cutting out some of the rear of the pipe for same effect, but I would worry about sitting in a campground with a wind from the rear of the van.

[themexicandoctor]

Pictures are better than a thousand words ...

[mkguitar]

Originally Posted by booster

but I would worry about sitting in a campground with a wind from the rear of the van.

that's the OP's call- it "seemed" to have occurred while driving
<Mike