Plumbing vents and negative pressure

[belfert]

I have some serious issues with smell in my bus from the toilet when traveling down the road.  If anyone uses the toilet while going down the road the smell from flushing will absolutely gag everyone else in the bus.  Running the roof vent in the bathroom doesn't really help.  I have used various chemicals in the tank to no avail.

I do have a vent going through the roof from the combined black/gray tank.  Last summer I did move the tank, toilet, and shower back about 8 inches or so, but 90% of the plumbing is the same.  The only thing I replaced was the trap for the shower.  I added an RV360 vent after the first trip, but that didn't fix anything.

It has been suggested I may have negative pressure in the bus which is sucking air in from the tank every time the toilet is flushed.  Any ideas how to fix a problem like this?

I only have a curtain for a door to the bathroom right now.  I suppose a real door might help, but that would only help contain the odor.

[HighTechRedneck]

I have a venturi style vent cap (the fin type) and it seems to work well.

If there is negative pressure inside the bus, it is going to be hard to overcome.  If you do put a regular door on the bathroom, that should also help isolate the bathroom from the negative pressure source.  If that wasn't enough you could use a low volume fan to draw a little air in either from the outside or main living area to introduce a slight positive pressure to the bathroom.

A ventilator in a closed bathroom will create negative pressure in the bathroom.  So if you close it in with a regular door and use a ventilator, you may want to have another fan of similar capacity bringing air into the bathroom from somewhere when the ventilator is running.

[loosenut]

Some trouble shooting questions: Has this condition been around since trip one?  Has it grown over time?  Are there some trips this condition doesn't happen?  Does it only happen when moving?  Has your diet changed?   The answers should help make the solution more specific.

My short exposure to bouncing plumbing has produced two stinky experiences.  A ptrap lost containment that adding water fixed.  The second was a caused by a friend and cured by adding Thetford brand blue goo.  The blue goo has worked so well that changing my toilet didn't stink up the bus.  There were a couple of weird black flying bugs I had to kill but no smell.

Mike

[belfert]

We didn't notice this until the two trips this last summer after the toilet, tank, and shower were moved.  It did not happen on the first traveling leg of the first trip last summer, but the tank was absolutely clean when the trip started.  We first had the issue on the way home (800 miles) after the tank had been emptied from our five day stay.  We had the issue again on the next trip for sure on the way home after emptying the tank.  I don't remember if it happened on the way there the second trip or not.

I suppose one thing to check is to be sure the vent is clear, but I don't think that is an issue.  Even if water was pooling in the vent enough to block it, the motion going down the road would certainly keep it clear of any water.

We're certain the smell comes from flushing the toilet as there is no smell otherwise from the shower or sink drains.

Edited: left out a word

[Chaz]

I tryed an approach last year that seems to work very well for me. I posted about it and some people were concerned it might not work, but it actually does very well.
I put two pvc tubes, one on either side of the top of the waste tank, and elbowed them over the side of the tank and down thru the floor. One has a 45* angle on the end when it comes out of the floor facing forward and the other is just cut straight off. It gives an exchange of air while going down the road because of the force of air into the tube or even when sitting still if the wind is blowing. The curved end one is - I think - 1 3/4" and the straight cut is 2", Im pretty sure.
I have taken my bus to concerts with as many as 12 people in it and have had zero issues....knock on wood. But I don't know about the negative pressure thing. Ya might think about it. Just a thought.
 Chaz

[Blacksheep]

Thru the floor? Tsk Tsk Tsk! That's a no no don't you know?
Ace

[Nick Badame Refrig/ACC]

Hi Brian,

I stumbled upon a smell from the tank that I never had before and I figured it out quickly.

After not using my shower for long periods of time, the trap dries up... Since all my plumbing vents are tied

together, it actually sucks the black tank fumes through the shower trap.. I just turn on the shower now

for a minute before setting off for a trip. Never have any smell anymore.

Nick-

[Len Silva]

If you only have a problem while on the road, you might consider an exhaust fan (bilge blower) sucking directly out of the tank.  That would keep a neg pressure in the tank even when the toilet is opened.  I would install it in a separate vent line from the main as it might impede the normal ventilation when it is not running.

[prevost82]

I did the same as Chaz .... I original had one vent at the end of the tank and was having bad smells going down the road. Then I install a vent on each end of the tank (tank runs across ways) through the bay floor and have very little smell problem.

I think what was happening was when I went around a corner the movement of fluid in the tank (the tank is baffled) would exceed the capacity of the vent and send the smells into the bus or suck the traps dry, depending which way the corner went. I also put sink stops in with a bit of water in the sink to make sure they are sealed and I have a large stopper for the shower drain.

If you have a powered vent you can also run the fan so it's pushing air into the bus (positive pressure) this also helps a bunch

[gumpy]

Yeah, I've had problems with mine since installation. I had a venturi cap on the roof and could smell gas. I think it might actually have been connections on the flexible hose I used for vent hose, but before I figured that out, I routed the vent to the air intake for the engine. So my engine sucks the methane in and burns it now. Well, then I had problems with it sucking the traps dry. Now, I've connected the roof vent back up along with the engine vent. I also sealed the flexible hose connections with plumbers paste and double clamps. The last trip was much better, but it was cold outside, so we'll see this summer if I have that issue fixed.

[Chaz]

Thanx Prevost 82.
Ace may think it's a no, no but, it actually works VERY well. "Proof in the pudding", as it were. I actually think turning the 45* backward so it will suck going down the road MAY work even better if you have negative pressure. But mine works great, so why change it.
  Later.
  Chaz

[Blacksheep]

Prevost82 YOU TOO?

What are all these busnuts turning into?

Doing all of this against the codes!

Shame on you guys!

I have NEVER had my traps Sucked dry although I HAVE had them evaporate dry while sitting here at home. As Nick has stated, simply run the water in the sinks and shower and the traps fill up sealing off any returning updraft of any nasty type smell!

Simple fixes for simple problems but those simple problems CAN become major problems IF you try and do everything by the book so to speak!

As I have said, sometimes you just have to look outside the box!

Ace... still smellin gooooooddd


CHAZ NO NO NO, I agree with you. That's the same exact way mine is and I was told I couldn't do it that way! You read my post wrong bud, but I agree! My vent even has a baloney cut on it to draw the air!

[Chaz]

Sorry Ace. I guess a smiley face would have helped me get your sarcasism . 

Oh by the way......... what codes? LOLOLOLOL 

We're just "Rebel's without a cause".

Chaz

[Blacksheep]

Chaz also my vent is directed rearward and has worked flawlessy!
Ace

[FloridaCliff]

Chaz,

First, Glad to see you back posting....

I also had some smell getting pulled in while driving, but only when the toilet was flushed.

My fix ended up being a simple tee on the top of the vent stack with a reducer from 2" to 1.5".

This caused the "venturi effect" and pulled the gases out.

Never had a problem while stopped.

Ace only likes the down stack because he refuses to say "upward(gas) and onward(over the roof)" 

Cliff