Building the 102DL3 (continuation of "Bumper" thread)

[richard5933]

There's no need to over think this. Just run a pipe from the tank up to the roof. Then put one of these on the top:

https://www.amazon.com/Camco-40595-White-Cyclone-Plumbing/dp/B003P64XU4

I've seen installations where the gray and the black tanks join together and share a roof vent. The whole idea is to create negative pressure inside the black tank so that when you flush the odor is being sucked up the vent pipe and not into the coach. The gray water has a p-trap which will prevent odors for the most part. The toilet will not - they just drop straight down into the tank. When you flush there is a direct connection between the stink and the coach. Amazing how much stink can come into the coach in just the time it takes to flush.

[chessie4905]

If you look how job johnnys are designed, the "input opening" is recessed a couple inches down into tank. The vent to roof is connected at very top of tank. That difference in elevation allows odors to go out the vent tube, even with the large opening under the seat that is mostly open. Excellent design.

[bobofthenorth]

Are you saying that actually circulating air through the tank would make it stink less? Seems a little counterintuitive, but maybe only hook one of those lines to the fan shroud and go through the roof with one of those FMCA doohickeys on the other?

I wouldn't go there.  Its a holding tank, not a composting tank.

The big difference from the boating world is the speed going down the road and all the weird pressure gradients that develop. I know that just venting out the roof with a modified residential stack is not ideal, but that's the way a lot have done it.  Its not the smell from flushing that gets you - its the stink that gets sucked into the coach going down the road. You're on the right track looking for a way to vent into a low pressure zone but the engineering is way above my pay grade.

[chessie4905]

Or you could pipe a vent into engine with a shutoff/ diversion valve. When engine is operating, valve allows fumes into air cleaner so engine can burn them. When engine is off, valve diverts to roof vent. A little more elaborate would be an additional diverter to gen set when it is running.

[DoubleEagle]

There used to be a product called "Stinkerator", if I recall correctly that was advertised in Bus Conversion Magazine back in the nineties, at least. This was a small fan in the vent pipe that ran constantly to create a slight vacuum in the holding tank to help keep the fumes going out the vent when flushing was going on. If it is no longer around, it might not have been effective in reducing odor leakage, or dependable. When looking for it on the Internet, I discovered that there are many such in-pipe fans of various sizes being used as battery box vents, and radon gas vents (in homes). It seems that having good vent pipes combined with a good sized fan that turns on when the toilet is being flushed, is the ultimate guarantee of keeping fumes out of the interior. The idea of having piping into the air cleaner sounds good, but would the suction be enough to draw the fumes out when flushing? Would the intake noise be transmitted down the pipes into the cabin? If you stand outside next to the air intake (at least on an Eagle) it sounds like a 2 cycle heartbeat.

Another solution to the fume problem with the RV style toilets, is to have a home-style toilet with a water trap, which would eliminate fume leakage (hopefully). Previous postings from people that have them indicate they are happy with them. The only problem is that they use more water even with the low-flow flush models.

[Jim Blackwood]

There are bilge fans like that but I wonder if the corrosiveness of the environment might drastically shorten their lifespan. Also I'm not sure I'd want to mess with the engine's induction system for a whole bunch of reasons. Like messing up the intake airflow and screwing up the air/fuel ratio. So I'll not pursue that idea here but who knows. Could be a useful idea. A lot will depend on how much room is there for routing. After all, PVC pipe is cheap. If I was going to try one of those I think it'd be the bilge fan even though it might not last long. Maybe tie it to the bathroom light or the ceiling fan.

That difference in vent height and inlet height could be worth something. I'm not altogether certain the gasses we're talking about here are lighter than air but I guess it couldn't hurt. Reduce the tank volume a bit, but only at the top.

Also thanks for the link. Those weren't available when I had the Coachman, and I made something out of a street "T" and reducers. It was fixed and didn't rotate but seemed to make a difference going down the road but nothing to amount to anything when parked. I hate to stick anything through the roof but might make an exception for that. I also figure that if it is drawing the fumes out continuously it about has to lower the concentration some. I have noticed that in open sanitation systems (sewers, pumping stations and such) where exposed to free oxygen, they still stink but not as bad as you might expect. Still, that black tank is some concentrated nasty.

This could take some trial and error. Towards that end I think I will try to avoid irreversible changes as much as I can, but that weathervane really does look like something that could do the job. Anybody have actual experience with those?

Jim

[richard5933]

Still way too complicated. Venting black tanks is pretty well an established science now. Even the high-end million dollar coaches just stick a pipe through the roof and put a device on top to catch the breeze, however slight. It only takes a very slight movement to get the thing venting.

There should be little problem with leaking if done properly. Even moreso on a bus than on a motor home since we have a metal roof to work with and to seal against.

Seems like the biggest problems come from lack of maintenance on black tanks. The devices on top of the vent pipe need to be kept clean and lubricated once in a while with a plastic-safe lubricant, the black tank should not be kept full (they stink worse when full) and A flushing once in a while to remove kling-ons from the sides of the tank so that solids are not above the liquid level.

The other things that seem likely to cause stink inside the coach are a bad/worn/dirty seal on the toilet flapper valve and/or water sloshing out of p-traps while driving.  A poorly sealed tank mounting seal can also be a problem.

[buswarrior]

Close the toll window when flushing underway...

Huge sucking out the toll window at speed.

Hard for the passengers to discreetly use the conversion outhouse... either tell the driver, or release the stink into the coach, either way, we'll all know you went...

Happy coaching!
Buswarrior

[luvrbus]

Holding tanks stink for a reason,you need to read about the gases in sewer they are lighter than air,passenger buses use a sealed tank with a suction fan when restroom equipped ,just walk behind one of those if you want a whiff of sewer gas.When people come to the shop for work if they are going to be here long I ask they drain and flush the tank my shop is 18 ft tall and in 3 days a 1/2 full holding tank will fill the shop with sewer gas 

[DoubleEagle]

Huge sucking out the toll window at speed.

Happy coaching!
Buswarrior

I can second that, I lost a nice set of Serengeti sunglasses with a leather case that got sucked out that window. It was like a mini tornado action. It would take a big fan in the bathroom to compete with that suction. 

[Jim Blackwood]

Aha. That's some critical information.
At one time we were beginning to discuss where the lower inside pressure comes from but didn't get very far with it. This is obviously one very large source. Leakage around the door might be another. Which makes perfect sense when you consider the bow wave that comes off the front of the rig and the eddies it has to create behind it. Any opening into those eddies will suck big time.

Now the vent line doesn't have to match that air volume, it only has to match the pressure difference it creates. That could be measured with a manometer as long as you have a consistent reference pressure to the outside. Aircraft do that with a pitot tube but it doesn't have to be dead accurate, it only has to be a steady reference. So you could cobble up something that would work, it could be as simple as attaching one port to the vent line and leaving the other port open to the bus interior. Then use the manometer to measure inside pressure (with the toll window open and closed) against the pressure in the vent line. This gives a scientific method of evaluating the effectiveness of any method used for depressurizing the tank. Was that ever done with the weathervane, or was it just evaluated by nose?

You can buy those U-tube manometers for next to nothing online and they will work just fine. In fact it might be a good idea to have one in the bathroom just so you know if it's safe to flush. Maybe as a reminder to tell the driver to shut his window.

Jim

[richard5933]

Remember, depending on the particular bus model all the high/low pressure calculations change if you're running the OTR HVAC system. When mine is running, even with the nose vent closed, the entire bus has positive pressure. If the HVAC system is running, there will be a rush of air out of the passenger door when I open it, even at a dead stop. Suction out the toll window in my bus gets even more powerful if the HVAC is running.

There is an air gasper on the pillar to the left of the driver in my bus. If the HVAC is running almost no air blows through the gasper, even on the highway. Turn off the HVAC and air will rush in when the gasper is open.

[buswarrior]

Quote:  Are you saying that actually circulating air through the tank would make it stink less? Seems a little counterintuitive, unquote

You have to know why things stink, before you try to combat it.

The RV industry want to SELL you stuff, they do NOT want a solution...

Some bacteria are your friend, some aren't. Most RV strategies quite purposely kill the friendly ones to perpetuate the myth, both saving money on build, and selling product to compensate.

You've got everything you need in this thread, roll the dice, pick your school of thought and get building!

Happy coaching!
Buswarrior

[Jim Blackwood]

The reviews on that Camco vent weathervane had a significant number who felt it was of little or no benefit as well as 2 or 3 who criticized it for sometimes operating in reverse, two who said it could direct rain water into the tank, and a fair number who complained of squeaking, discoloration, warping and then the largest complaint by far, simply blowing off when on the road. (coming apart) They also generally described a 1-1/4" or 1-1/2" vent pipe.

The alternative seems to be the 360 degree siphon vent which is not dependent on wind direction but probably does not generate as much suction either. So at this point I'm thinking a 1-1/2" pipe with a 360 siphon vent cap and below that a bilge fan switched by the bathroom light, coming through the rear cap, and then perhaps a second somewhat smaller pipe attaching to the radiator fan shroud. That way one or the other or both can draw vapors out depending on circumstances as well as circulating fresh air through the tank.

Concerning the weight of sewer gases, two are heavier than air, carbon monoxide and hydrogen sulfide, both of which are poisonous and will accumulate in the tank and vent stack, exiting at the toilet if they can. The ammonia, methane and such are lighter than air and will go up the vent. Fresh air in the tank will reduce the production of Hydrogen Sulfide which is the primary odorant. Methane and carbon monoxide are odorless.

Jim

[chessie4905]

Yeah, rain water getting into tank.....come on.