Black tank smell only at 65 MPG

[DonTom]

How come I can often smell the blackwater tank when the windows are open on the freeway at 65 MPH? I understand there's a

vent to the roof, but at 65 MPH and 24 feet behind the driver & passenger, I wouldn't think smelling that would be possible

at 65 MPH.

The strangest thing is, we never smell it at slower speeds. Not even when driving on bumpy road that should shake things up

in the tank.

No smells at all when standing still, inside or out. Seems to only happen when at freeway speeds, and sometimes quite strong

so we close the windows and use the A/C. It's quite warm up here, both day and night.

-Don- (in BC, Canada, boondocked at a rest stop near the Alberta border)

 

[Gypsy Rovers]

Don, I suspect that 65 MPH is the speed at which the turbulence from the front of the coach is curling back around in the area of the vent and bringing it down to the side windows.  Stopped and slower don't cause the same vortex's so no smell then.

Enjoy the warm weather in BC & AB, it's unusual for this time of the year.

Cheers
Dale

 

[regularguy]

I would try putting a spoiler behind the vent. You could cut one out of a piece of flashing. Cut a piece, make a circle to fit over the vent pipe, put a bend in it, bend the edges to support the spoiler when the air hits it, place an aircraft style clamp over the vent pipe to hold the piece in place. If it works then you can make something permanent. That would create a vacuum just behind the spoiler which should direct the air rearward...

 

[rbell]

I put one of these Camco vents on a travel trailer I used to have. We would get a slight smell when parked and the wind was just right. After it was installed I never noticed it again.

 

[Gary RV_Wizard]

There is another possibility, i.e. the venturi effect of the wind blowing by the open window is sucking fumes from inside the coach. Just a little bit of low pressure inside is all it takes. That may be gray tank odor too, rather than black. It is often mistaken.

If it is indeed black odor and the problem is low pressure inside, the likely source is the toilet overflow, which is a small hole under the rim of the toilet that would let water drain into the black tank if it got that high. It has a "P" trap in the overflow but it often gets dry and can let fumes escape back into the RV.  If it is gray smell, the problem may be an anti-siphon valve in a sink drain line, which can leak smelly air back into the RV if the "flapper"  in the valve is weak.

 

[jeverden]

Load the tank up on your septic tank treatments!

Kill the smells that way.  Or install one of those vent covers that let air down and out to rid your rig of gasses.

Cut down on the mexican food!

lol

Jay

 

[DonTom]

I put one of these Camco vents on a travel trailer I used to have. We would get a slight smell when parked and the wind was just right. After it was installed I never noticed it again.

Thanks, I will give it a try. It cannot hurt. I think anything would be an improvement.

BTW, here, there is no trace of the smell inside with windows closed or outside when stopped.

And BTW, both  tanks (black & gray)  were emptied the same day, just before  we had the worse smell at 65 MPH leaving Spokane.

-Don-  (in Red Deer, Alberta)​

 

[Gary RV_Wizard]

There is a basic flaw with those vents: they can't suck fumes OUT unless there is a way for air to get IN somewhere else. And if there is a leak somewhere else to let air in, you will have fumes escaping anytime there is not suction on the vent pipe. Fix the leak and you don't need the turbo vent.

 

[Mc2guy]

If it is indeed black odor and the problem is low pressure inside, the likely source is the toilet overflow, which is a small hole under the rim of the toilet that would let water drain into the black tank if it got that high. It has a "P" trap in the overflow but it often gets dry and can let fumes escape back into the RV. 

That is the first time I have every heard of this secondary drain!  Wow, I learn something new on this site every day.   How do you make sure the p-trap has water in it...my toilet is a year old and has never been filled all the way up with water so I assume this secondary drain has never been used.  Could that mean it has never had water in it? 

 

[Ned]

We have a Sealand Traveler and the company gave away rubber plugs to put in the drain holes in the bowl to prevent the odor problem.

 

[Mc2guy]

Mine is a Thetford...not sure of the model.

 

[Gary RV_Wizard]

If there is a hole under the rim somewhere, get a small hose or funnel and pour in a few ounces of water. Or stick a wad of plumber's putty in the hole and forget about it. Newer toilets may not have the drain, which often caused odor problems and RV toilet overflows are a rare occurrence (only happens if the inlet valve fails by breaking apart inside).

You can be sure the guys at the factory did not pre-charge the drain line with water for the P-trap, nor did the PDI guy at the dealer.

 

[John From Detroit]

ne thought.. You said it only happens at 65mph (your RV is likely recommended only to 55, but let's not discuss that) at 65MPH you are very likely behind someone else..

Also, your engine is cranking out a lot of revs. which means your alternator, if unregulated, may be "over voltage"

Overcharging of batteries can release Sulfur Hydroxide (H2S) which.. Of course.. Is the odor of rotten Eggs.. Likewise if the person in front of you had high-sulfur fuel it can smell like rotten eggs... And I have seen people mistake this odor for sewer smell many times.

I really don't like chemicals in the tank save water, and perhaps some Calgon and Dawn regular dishwashing liquid.

Dump, add 1/2 cup each of the above, plus 5-10 gallon water, drive,  park, and dump again.

 

[Mc2guy]

I have definitely had this happen at speeds from 50-65mph and I can assure you it isn't from the batteries.  ;D 

First, I have a ScanGaugeII and constantly monitor alternator voltage.  It is stable between 13.4 and 13.7.  Second, it doesn't take a rocket scientist to figure out where the smell is coming from...just open the door to the "loo" and it is pretty obvious!!!

 

[DonTom]

There is a basic flaw with those vents: they can't suck fumes OUT unless there is a way for air to get IN somewhere else. And if there is a leak somewhere else to let air in, you will have fumes escaping anytime there is not suction on the vent pipe. Fix the leak and you don't need the turbo vent.

Gary,

We went to a couple of RV stores in the Edmonton area today to ask about this problem. They both say they sell a lot of these thingies for the exact same problem I am having. Please read the FAQs there, I would like to hear your comments about what they claim.

One of the places, Leduc Alberta RV LTD, said they can install it for me, but they have to order it first on Monday from Calgary (where we were yesterday, but didn't stay long)!) and have it by Tuesday. We may stay here in the Edmonton area at least that long.  Installed is about a hundred Canadian bucks.

If it works, I think I would rather do that than trying to find an air leak in the black water tank! I wouldn't know where to start and it sounds like such a dirty job!

And if these guys are telling the truth, there sure are a lot of RV's with the same problem, as both places say they sell these things like hotcakes and often run out of them as they are now.

BTW, there sure are a lot of RV part  places here in Edmonton. We passed up many RV parts shops getting here to the most crowded RV park we've ever been in.

-Don- in very crowded <no empty spaces on this warm Friday night, we got the last spot!> Devon RV Park, Devon, AB (SW Edmonton)​

 

[Alaskansnowbirds]

Installed is about a hundred Canadian bucks.

If it only does it at 65MPH, I'd put the hundred bucks in the gas tank and slow down to 55 or 60.

I really don't think a new vent cover will fix your problem.

 

[seilerbird]

You have a problem and everyone here is trying to solve the wrong problem. Your black tank should not smell under any circumstances. Trying to figure out a way to stop the smell at 65 doesn't solve your problem. You need to stop the smell period. My suggestion is to go to a dump station and completely dump the black tank. Then take a flashlight, turn off the water and open the valve at the bottom of the bowl by holding down the flush lever. Look in your tank and see if you see the dreaded brown pyramid. If you see any brown at all then you need to do a great job of flushing your tank. If you have an external hookup to flush the black tank that might not be enough. You should put a high pressure nozzle on a garden hose and flush from the inside via the open valve in the bottom of the toilet bowl. It will take at least 10 minutes to make sure you have gotten all the stuff out.  Or else you could have your black tank removed and professionally cleaned.

 

[DonTom]

If it only does it at 65MPH, I'd put the hundred bucks in the gas tank and slow down to 55 or 60.

I really don't think a new vent cover will fix your problem.

A hundred bucks up here has not filled up my 55 gallon tank yet. BTW, this entire trip I have been checking my MPG. Better than 9 MPG average the entire trip, even with a lot of generator running at times.

Gasoline is more than a dollar per liter in the Southern part of AB, but just under a Canadian buck up here near Edmonton. Gasoline is more expensive in BC than in Alberta. Cheaper than we expected. Being from SF, gas prices in Canada are almost reasonable. But we were shocked that food in restaurants up here cost more than in London and more than twice what we're used to paying in San Francisco.

Anyway, the guys who sell them say they work great (salesman never lie, right?)  ;D.  So does a guy in this thread. Do you know anybody who has had the problem who has tried such a vent where it has NOT helped?

I might  have to spend a hundred bucks just to report back how well it works!

-Don- Devon, AB, Canada​

 

[DonTom]

You have a problem and everyone here is trying to solve the wrong problem. Your black tank should not smell under any circumstances. Trying to figure out a way to stop the smell at 65 doesn't solve your problem. You need to stop the smell period. My suggestion is to go to a dump station and completely dump the black tank. Then take a flashlight, turn off the water and open the valve at the bottom of the bowl by holding down the flush lever. Look in your tank and see if you see the dreaded brown pyramid. If you see any brown at all then you need to do a great job of flushing your tank. If you have an external hookup to flush the black tank that might not be enough. You should put a high pressure nozzle on a garden hose and flush from the inside via the open valve in the bottom of the toilet bowl. It will take at least 10 minutes to make sure you have gotten all the stuff out.  Or else you could have your black tank removed and professionally cleaned.

You know, you could be right.  When I left the RV Park in Spokane, they had everything but a dump at each site. Tom & I left at the same time, him to return the rented car to the Spokane International Airport and me to pick him up in the RV (a real hassle, compared to here in Edmonton, where they picked us up to get the rented car). We were pressed for time, but I went to the RV park's central location to dump the tanks first. I didn't have time to clean out the tank. Just dumped and left.

BTW, how well do these thingies work?

-Don-  Devon, AB, Canada​

 

[seilerbird]

I don't know how that thingy works. But it looks interesting. I have a clear elbow between the outlet and the hose and it is amazing how much brown stuff comes out after the tank is empty and I start the rinsing process. Another thing to remember is to put several (I put in around 10) gallons of fresh water into the black tank after I am done rinsing.