Waste tank vent location

[Nel]

I started my plumbing in my 4104 from scratch after gutting everything previous , I may have to relocate the waste vent tube at the top of the bus , is it better to keep in near the rear of the bus or any other tips . I am using pex thru out for the water lines.
also I'm thinking of using one waste tank for black and gray . Good , Bad?     Thanks

[bevans6]

Top of the bus in the middle is best.  The farther forward you get on the roof the lower the air pressure when driving so fumes naturally get sucked out better.  The farther back you go the more the air stream reattaches to the skin of the bus, and the last four to six feet is actually a high pressure area.  If you open the driver's window of the bus, air gets sucked out, if you open the rear passenger window the air gets blown in.

Brian

[Scott & Heather]

Nel,

we ran our vent out the top of the tank and then immediately down through the floor of the coach luggage bay. 5 years fulltiming, never had an issue or has smell problems with this arrangement. Also, this provides a safety overflow so you're not backing up sewage into your shower if your tank overflows.

We have a 100 gallon black/grey combo. Would never ever go with a dedicated separate black tank or grey tank. This arrangement is perfect. It keeps the black sewage fluid and on the move with added shower and sink and washing machine water. When we are boondocking, I have valves on every drain to drop the grey water to the ground if need be and just use the tank for the toilet. We can go weeks like this if need be. Just our way.

[RJ]

Nel -

My coach is set up similar to Scott's, with a 100 gallon grey/black holding tank mounted in the rear bay biased to the curb side.  The 8kW genset sits on the driver's side, along with the drain plumbing for the tank.  Also in the bay is a 100 gallon fresh water tank, the 11 gallon hot water heater and two diesel-fired Webasto forced air furnaces (which are being cantankerous right now. . .)

The holding tank's venting is also similar to Scott's, but slightly different.  It comes out of the RR corner top of the tank then turns and goes out thru the rear bulkhead wall and drops down to the bottom of the bulkhead where a 45^o elbow facing rearwards completes the venting.  (I can share pics, if you'd like - send me a PM with your email address.)  Again, like Scott, no odor issues, so it must work.

My holding tank procedure may have some bearing on this too.  I don't drain the tank until it's at least 3/4 full, and when I do drain, and if available, I completely refill the holding tank twice to rinse (tank has a fill line separate from the main house system fill.)  After draining and rinsing, I have a couple of empty gallon milk jugs which I use to add five gallons of water to the tank, then drop in one of those inexpensive septic tank enzyme balls you can get at any hardware store.  Much cheaper than the stuff you find at the RV store, and, IMHO, far more effective.

FWIW & HTH. . .

[eagle19952]

mine is like Scott and RJ's works very well.Any mishap has only overflowed clear liquids... easily seen and remedied.

[Scott & Heather]

Don, you must be drinking plenty of water....

[luvrbus]

The Hydrogen Sulfide caused by decaying matter causes the sewer smell keep your tanks clean and won't have the smell.Methane gas is always going to be present and has no odor.I vent through the roof RVIA code. I just have a cheap Ridgid sniffer from HD it always pickups the Methane gas at any vent.I have seen 1st hand what Methane Gas can do and I want no part of it JMO we all do it different though       

[Nel]

Thanks for the responses Guys, I will use all your suggestions, while I'm putting it together here, Nelson

[TomC]

On my bus I have a 130gal fresh, 85gal gray, 45gal black. I like it since the gray doesn't fill the black tank needlessly. My transit has limited space and those were the biggest tanks I could squeeze in. I have my main drain on the left side and have a gray tank drain to the street on the passenger side if my gray tank is full and I can pull up to a street drain to discretely drain it. I have three roof vents-one for the toilet, one for bathroom, one for kitchen. I like the system so much, I'm repeating it in the truck. But increasing the tank size to 200gal fresh, 115gal gray, 69gal black. Why-because I have a 50,000lb gvw with 38,000lb rear tandems.  But I doubt I'll weigh more than 35,000lb when done. Good Luck, TomC

[eagle19952]

Don, you must be drinking plenty of water....

i only make sinkers....  

Seriously, (i have operated many extended aeration sanitary waste water treatment plants at remote drill rigs in the oilfield),, the sludge that forms in a static tank sinks and clear liquids are on the top... that is the principal behind waste reduction... ... i spent a lot of my time consulting and operator training to conform to EPA and DEC standards for effluent discharge ...but i digress

Atypically (and very basic):

[Iceni John]

Another possible option to consider is to have two vents per waste tank.   This way you can have a through flow of fresh air in each tank, which should help the aerobic bugs to do their thing.   I have a 115 gallon gray tank and a 65 gallon poo tank that each have two 2" vents in diagonally opposite corners  -  the poo tank's rear vent goes straight up to a West Marine louvered hose vent on the side of the bus and facing forward, the poo and gray tanks' forward vents are joined together, and the gray tank's rear vent goes down to road level with a rear-facing venturi just ahead of the differential.   When driving, the poo tank's hose vent scoops in fresh air that blows through the poo tank and gray tank, then is sucked out of the gray tank by the venturi effect.   When parked, the airflow reverses, with methane and smells exiting from the poo tank's upper vent, and fresh air being drawn in from ground level.

Like Tom C, I also have a 1.5" dump valve for my gray tank just ahead of the passenger-side rear wheels, and a transfer pump to move excess gray water into the poo tank.   The poo tank has an inlet directly above its main dump outlet, so either gray water or fresh city water (obviously protected with check valves!) can be jetted into the poo tank to help break up any Mounds Of Doom or stalagmites that are growing near its dump valve, or to help rinse it after dumping.

John