Holding tank vent

Nova Eona · April 30, 2021, 11:04:04 AM

Quote from: Dave5Cs on April 30, 2021, 09:20:10 AM
Seriously? You might want to rethink this one. As Clifford said above that is Methane gas coming out there. Just takes a spark and the right timing and batteries sometime have those kind of events.

The pipe terminates right next to the louvered vent on the door, developing a methane concentration high enough to be problematic seems unlikely. I could easily elbow it into the wheel well to the side, but I've been rebuilding the water system over the winter so I have yet to even try it out properly yet.

Glennman · April 30, 2021, 01:17:45 PM

In all my years as a mechanical contractor, I cannot tell you how many times people (customers) would ask if their roof would leak, or it there was any other way to vent a gas unit without cutting holes in the roof. I would explain to them that probably every house in the world (?) has multiple holes cut in their roofs for plumbing vents, gas vents and other types of venting and penetrations. It is such a common thing that it should be no problem at all. Having been in that position, I would install 10 vents out the roof of my bus, and then sleep like a baby.

Plumbing codes require that vents to go out the roof. I don't know what applies to RV's (there is no doubt some code out there regulates RV plumbing). I would suggest going out the roof, and then devising a way to create a suction effect for driving so that you don't cause the tank to become pressurized while underway (such as was suggested in other posts). Enjoy!

Jim Blackwood · April 30, 2021, 01:33:44 PM

Here we go again, huh? Yes it's true that methane gas is lighter than air but guess what, it isn't the methane that stinks. It's both colorless and odorless. So while it can be a fire hazard if concentrated, it isn't what makes your waste tank stink.

Those gases are heavier than air. So you might have to re-think your strategy a little. To get them to move out the top of a roof vent there has to be some sort of airflow through the tank. And to encourage aerobic decomposition which gets rid of those stinky gases there needs to be airflow.

Also, if you let the stinky gases build up in the tank and you have a roof vent only, then they will eventually pile up in the vent tube all the way to the top and when you open the flush valve just the weight of the stinky gases will make them run back down the vent tube and push stinky gases out the toilet.

There are ways to solve this but what's most needed is a method that runs fresh air through the tank all the time both OTR and curbside and has no energy cost. That way the anerobic decomposition does not produce the stinky gasses in the first place and then they don't accumulate.

Ideally airflow would be out of a roof vent when curbside, and a suction would be pulled against the tank OTR. The best way to do that? Hard to say really. Lots of ideas have been tried.

Seems like it'd be a good idea to locate a low pressure area when moving, like at the rear of the bus, maybe up high. Would convection be enough? IDK. But it seems like a bilge fan tied to the bathroom light switch could help a lot. Just some ideas.

Jim

Nova Eona · April 30, 2021, 01:42:50 PM

Sounds like a good application for a small solar panel tied directly to a fan somewhere.

richard5933 · April 30, 2021, 02:25:29 PM

Pretty sure that none of us hold the waste in the black tank long enough for bacterial decomposition. I know that I dump ours long before that happens.

The reason for the vent is pretty much to provide for a proper flow of waste into the tank. If the air can't get out, new liquid can't go into it.

Tedsoldbus · April 30, 2021, 04:54:07 PM

My two "T" pipes come out in line with each other and 4 inches apart. I agree with " Let that methane go up and out". Only flaw is my pipes are near the vented roof/fan like most. When I forget to close the roof vent at a campsite and do not have the fan on, and a breeze comes from behind the bus, the roof air scoops it right back into the bus. If you already have a roof vent, keep that in mind before you punch holes in the roof. Lots of ways to waterproof those pipes on the roof. Worry not. Good luck with it!

6805eagleguy · April 30, 2021, 05:23:52 PM

Quote from: buswarrior on April 30, 2021, 08:37:19 AM?

Having the driver's toll window open when someone steps on the pedal... various busnuts have been able to splash the occupant of "the little room" ...

Yes that happened. Didn't relate it to the window tho. We have a 2 inch vent. What exactly would a second vent do?

luvrbus · April 30, 2021, 06:09:25 PM

Methane is not a friendly gas it displaces oxygen and will get you I saw a worker pulled from a 4 ft deep x 4 ft round manhole the methane killed so it is up and away for me now

buswarrior · April 30, 2021, 06:51:46 PM

Quote from: 6805eagleguy on April 30, 2021, 05:23:52 PM

Yes that happened. Didn't relate it to the window tho. We have a 2 inch vent. What exactly would a second vent do?

The second vent is to allow for lots of air flow, in and out, of the waste tank. The bad smells come from a lack of oxygen, lots of air, the wrong bacteria don't thrive.

This is aimed at stationary issues, not so much the ram air stuff.

Those who have lots of available oxygen in their waste tank, do not have bad smells.

The splashing? That is a powerful option available to the driver...with great power, comes great responsibility...

Happy coaching!
Buswarrior

Jim Blackwood · April 30, 2021, 08:14:28 PM

Quote from: richard5933 on April 30, 2021, 02:25:29 PM
Pretty sure that none of us hold the waste in the black tank long enough for bacterial decomposition. I know that I dump ours long before that happens.

Bit of a misconception there since the bacterial decomposition actually began before you even ate the food. You'd really be amazed at how fast liquification occurs. In the city solid waste never ever shows up in the sewer. Only black water. How long do you think it takes to go from an apartment complex to the street?

Quote
The reason for the vent is pretty much to provide for a proper flow of waste into the tank. If the air can't get out, new liquid can't go into it.

Not really true either. A properly designed system will not stink. One with only one vent only large enough to allow inflow will always stink. You can only hope to contain and disperse it.

Jim

chessie4905 · May 01, 2021, 12:30:23 PM

Go study the newer job johneys they have roof vent and even with toilet seat up, no odor.

Jim Blackwood · May 02, 2021, 09:05:21 AM

Um, not exactly right? They have a chemical smell and have you seen the stuff they leave in those when they drop them off? No decomposition of any sort going on there would be my guess. A foul witches brew of some sort. But, if you'd rather cart around a few carboys of that stuff in your spare storage space why not? Oh, and with that open toilet there's plenty of air available for aerobic decomp if it ever did get started. Without that who knows what they would smell like? Not sure exactly what you're trying to say here.

Jim

chessie4905 · May 02, 2021, 09:12:38 AM

I see that. The seat area is domed and vent pipe comes from that area through roof. With seat up, no fumes come up from that area even when 3/4 full or being used. Natural draft. Big improvement over old ones.

silversport · May 02, 2021, 10:42:54 AM

1 1/2" PVC pipe (one for both tanks) through the roof, 30 plus years no leaks with a T cap on top for venting, has worked for me.

niles500 · May 02, 2021, 12:11:49 PM

I like the idea of a sweep T on top with the sweep to the rear creates a venturi effect