Black tank vent

[gus]

John,

My 4104 has the same setup except only one 1.5" vent tube. Two tubes are better but I didn't have that much space. Only one small tube causes the traps to be sucked dry during fast dumping but the solution to that is to dump slower.

Having that overflow feature is an added advantage - just in case. That is far better than any other overflow options!!

[dougyes]

Our previous venturies on the roof were targets for tree branches, and always broke. We ran the new vent flush with the roof, sealed with silicon. Works well. If a few drops of rain get in- no big deal. We used flexible 3/4 hose connected to a brass barb fitting siliconed flush with the roof.

[JohnEd]

I had a horrific odor, think warfare, problem that eventually proved to be a hairline crack in a PVC sewer line that ran up behind the toilet to the roof.  It was the black water tank vent.  Did I mention that it was a "hairline crack"?

You get a serious "suck" going and it doesn't take much of a hole to cause pause.  

It sounds like you have less of a leak when the interior is subjected to the "open toll window" thing.  The interior should be under some slight negative(suck) pressure even with that window closed unless you have a lot of leaks on the front surface of the bus that are mildly pressurizing the interior.  With the toll window closed try going back there and sniffing around.  If there is no odor at all you are pressurized.  If you have a slight odor....you are in luck.  While underway, get a length of 2/8 hose, 4 ft, and start sniffing all the joints in pipes and the toilet seal and pipe runs.  You will eventually find the gager and the leak.

You are supposed to have . read that as MUST, a 2 inch ID PVC vent pipe from the tank to the roof and that run must be verticle and have no bends.  I once read that a single 45 degree bend was max but that sounds excessive to me.  I also read once that there needs to be two vents from the black tank....dunno.

Ace has said before that his vent goes out the bottom of his bus.  He is certainly proud of that vent and especially so in that it "flies" in the face of all the instruction and common logic.  Nearly all, anyway.  God bless him and his unusual success.  There are a few thousand Knuts on here and I don't recall Ace getting another nod from anyone else that has run their vent out the bottom.  Not saying a few don't exist, now, outta 3 thousand souls.....only say'n!!!!  Were I Ace I wouldn't change my bus as long as that design works....why do so.  Given that truth, I would do it like every instruction and spec says to do it at the outset to avoid problems.  Run it out the roof like the "big kids".  There are all kinds of unconventional stuff happening out there but who wants a Dr. that proposes to take your appendix out through your ear???   Specially if your problem is with your gallbladder.  All said and done, those unconventional folk enrich our lives and inspire fixes unique to "special" problems.

If you are just completely flummoxed by this problem I have a suggestion:  Go to a AC specialist and have him plug your roof vent, add freon to your waste tank through a jerry rigged coupler , and run his sniffer around till he locates the "freon leak".  And continue till he is sure there isn't a second leak.

You might simply pressurize the system sitting there and do the nose sniffer thing, also. We are talking a half pound of pressure don't forget.  Don't want your potty bounce'n off the bathroom ceiling.   The crack in my pipe was on the side to the wall and it too me months to find it and the fix cost less than a dollar.

Fun talk'n with ya,

John

[JohnEd]

If you use a small vent hose then when you flush you will pressurize the black tank and there will be a "puff" of gas back into the coach.  BOOOOOO!

In my system I have 2 inch vent house.  When I flush I can stand on the pedal and peer into the black tank with a flash light, it is a straight drop, and see the water level.  NOTHING comes back up to discourage me.  The air gets flowing in the right direction out the vent and can't change.  Mind you, I have never positioned a brick on the dump pedal to test how long it would take for the gases to reverse flow.  Just not a curious kinda guy or even that patient.

Good luck,

Use the correct design, vent pipe size, and DUMP FAST.  Nobody likes to dribble shix.

John

[Iceni John]

I've heard that a black tank's vent should be large enough to let fresh air into the tank, to allow the aerobic bacteria to do their job in breaking down the contents (which supposedly will reduce the smell).   Some folk here are using quite small black vents, obviously sufficient to let air in as the tank is dumped, but maybe not large enough for this aerobic thing to take place.   So, who's right?   Do the small-vent folk have smellier black tanks than the large-ventists?

As for the Through-The-Roof or Not-Through-The-Roof controversy, I have an idea which I want to run by you.   Instead of maybe six roof openings (two vent pipes, the electric cables from PV panels, hot water pipes to and from solar water panels, and a cold water line to allow easy washing of the PV panels), I'm thinking of just one large-diameter pipe which would also be open at its bottom end under the floor.   In other words, you would be able to look all the way through this mega-pipe, and see either sky or road.   This pipe would simply be a conduit, inside which would be all the individual pipes and wiring that need to go up to the roof.   Any rain would simply run down inside it and drain out the bottom straight onto the road.   This conduit-pipe would need to be about 6" diameter or larger, but could easily be hidden inside one of the closets.

Is this a daft idea, or would it work?   It's going to be a while before I start building my interior, so I've got plenty of time to think about its pros and cons.   Has anyone here done anything like this?

Thanks, John    

[Ace]

Well John, simply put, my vent going down works, has worked and has given us no smell under any condition. With that said, do you think if it didn't I would continue to come on here and publicly promote it?
I guess its just the same as when I used a round aluminum fuel tank to build my black tank. Ya'll said that couldnt be done too, or the fact that I hung it from the main floor frame structure, which couldnt be done, or have it mounted sideways rather than front to back, which couldn't be done, all for obvious and deadly reasons but I did and everything works just fine.
Think outside the box and not always what the book says.
Yea, i'm proud because it was cheap and it works....simply put!

[papatony]

As some one raised by a building contractor and worked with pluming for forty years the purposes for a vent pipe is to allow air to enter the pipes so that the water can suck the air behind it into the tanks. One vent is good for these buses (2 " ) and it must be higher than the highest water dump. There should be no more than a 45 degree turn in it.

[brando4905]

My tanks are vented through the bottom also, only problem I've had is when the toilet valve quit sealing. Also have a power vent on the vent line for a little extra venting.

[buddydawg]

I have my 90 gallon gray/black tank vented through the bottom.  One 2" vent on each side and have had no odor issues inside the coach.

[bevans6]

For those with bottom vents, do you simply ignore the trapping of methane, do you believe methane doesn't exist, or do you think the methane somehow gets out the vent that you do have?  Or do you think that letting the methane into the bus when you flush the toilet is a good option, presuming the toilet is a typical sliding trap type flush system?

Methane, also called swamp gas, is colourless and odourless, so you won't know it's there.  But it assuredly is.  It's not toxic, unless it is present is sufficient volume to displace oxygen, but it's quite flammable.  Whether it would be possible to get sufficient volume inside the bus from gas leaking up into the bus from the toilet is another matter, I suspect not.

Brian

[Chaz]

Hey Eddie,
  I'm not going to get into a "back and forth" with others and the "codes". I just feel mine has natural venting capabilities and I'm fine with that. If they feel I'm too far outta the box, I'm ok with that. (hell, I'm an artist!!  ) And I'm a firm believer in Einstein. Look below....

  Sorry, I digress and I said I wouldn't. Nuff o' that.............

The "T", as it were" that I think I you are talking about, is another one of my creations.        (I'm just full of 'em!! or "sumthin", not sure what) Anyway, what it is, is a "t" that is adapted down on the horizontal opening to a garden hose size fitting with a on off valve on it. And below that, before it goes into the tank, is a large ball valve. The reason for this is if I am camping (and for all the "sticklers") where appropriate (whether they think so or not) I can close the big ball valve and open the hose valve and let the shower water (only) flow to an appropriate place, be it what it may. It saves on filling the tank with too much water too soon.

Does it work? You bet. Have I "HAD" to use it? Nope. I have not been so fortunate as to be able to be in my bus for that long.
I did that as a compromise to having two waste tanks, which I really wanted initially.

So there you have it. Hope I helped and did not get into any MORE trouble. 
  Chaz

[Ace]

Just to prove that a vent does NOT have to go thru the roof, check out a "studor" valve.  Its a small 2 inch valve that vents the line. We removed our they the roof black pipe vent in our house and installed one of these in our kitchen. It works, per a plumber wuth many years experience and its the ONLY vent on the house. No smells, no slow drainage, nada! If you can do this in a house that doesn't move, who says you can't do it in a bus? Just saying, unless of course the methane gas has are my brain up over the years.
This is just one example.
Why is it almost every topic results in a debate? Tried and proven but were still wrong. It's not the internet bully running people off, it's this exact thing. People beat a non issue to death and they are only posting what they think rather than what they have actually done. Read all your books, laws, and codes but remember, they are only there because they are. You would have to have a hell of a lot of methane gas built up to cause an explosion and who keeps their tanks full all of the time? I sure dont!

[luvrbus]

The AAV (studor) works different it sucks air in does not vent into the air, mobile homes have used those for years with one at every fixture to keep the water seal from being sucked dry,lot of RV's use the AAV but still vent the tank

good luck

[Van]

Is there any advantage to plumbing the Methane back into the engine intake?

[Oonrahnjay]

Hey, Ace, have you noted smells around your bus on the outside while parked?  Does your "low vent" need to be in an area of low-pressure outside the bus (of course, that isn't hard, most areas under the bus are low-pressure) - does it pull the water out of the sink traps when the bus is moving?  Thanks.