Drain Venting

[Doug1968]

Fellows,

My coach layout has the toilet and a bath sink located on the passenger side of the bus. On the other side the shower and another sink are located.

a) The toilet is a direct drop, the sink located by the toilet has about a 4 foot run (1-1/2" ABS).
b) The shower, located on the driver side has about a 3 foot run (1-1/2" ABS) and the sink on the same side will also have a 3 foot run (1-1/2" ABS)

My question, what needs to be vented?

I plan on having a 1-1/2" vent from the gray and black tank running to the roof. Not sure there is a need to vent the other runs.

I'd like your thoughts.

Thanks,

Doug

[bevans6]

the shower and both sinks should be vented, if only by AAV's, and the tanks definitely need to be vented up to the roof.  One vent can be combined for units that are within a few feet of each other, and the main vent up to the roof can combine with the drains in some circumstances.

Brian

[Tenor]

I only ran vents for my tanks and have had no problems.  My bathroom is all on the passenger side, and my kitchen sink is on the drivers side.  I vented the gray tank through the wheel well and have had no problems with odors or otherwise.  I ran the vent for my black tank behind the fridge and out through the refrigerator's roof vent.  It kept holes in my roof to a minimum. 

Good luck!

Glenn

[robertglines1]

Does any one else have problems sucking water out of traps with only one vent? I just slow dumping valve rate of discharge..do I need more vent area?  Bob

[redbus]

Bob Yes you need to put the AAVs in the drains next to traps.

[robertglines1]

AAV is that the same size as sink drains? just T below trap?  Bob

[luvrbus]

Bob, the AAV's go above the trap if you have a run of pipe with more than 1 fixture on the run all you need is 1 AAV for that run


good luck

[Sean]

Code says every fixture must be vented, except for a direct-drop toilet.

AAV's are permitted only as secondary vents -- all waste lines still need to be vented through the roof.

If you have fixtures on both sides of the coach, that will mean you will have vents on both sides, too.

Wet venting is permitted, so long as the rules about number of fixtures and sizes of drains are followed.

I strongly recommend you get a copy of the book, NFPA-1192, about $30 on-line.  Not only will this tell you about drain, waste, and vent lines, but also LPG, emergency exits, ventilation, and a host of other RV topics -- everything but electric power, which is covered in a different code.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[luvrbus]

Codes must not apply to mobile homes and RV's saw 100's with only 1 AAV on a run with more than 1 fixture and fwiw they worked 


good luck

[rv_safetyman]

Well, I hated to admit my ignorance (you all know about it anyway ), but I had no idea what an AAV was.  A quick search got this explanation at WIKI:

Air admittance valves (AAVs or Durgo valves) are pressure-activated, one-way mechanical vents, used in a plumbing system to eliminate the need for conventional pipe venting and roof penetrations. A discharge of wastewater causes the AAV to open, releasing the vacuum and allowing air to enter plumbing vent pipe for proper drainage. Otherwise, the valve remains closed, preventing the escape of sewer gas and maintaining the trap seal.

My system does not have these.  I have tank vents going to a "Y" and a single pipe through the roof. 

The only issue I have is that the washing machine "P" trap drys out once in a while.  I ran small tubing to the top of that drain and have a valve on my manifold dedicated to that line.  Every once in a while, I will open that valve and fill the "P" trap.

Jim

[bevans6]

The idea of the AAV's or a proper vent on a sink drain line is that they promote proper drain operation by allowing air to rush in behind the water.  That lets the drain actually drain, and allows the residue of water left behind to seal off the P-trap.  Otherwise suction would pull that water out of the P-trap and you get fumes coming back.  AAV's  can be installed under a counter but as high as possible, and they are installed with a tee fitting and a vertical riser after the P-trap.  Typically you install a proper vertical vent or an AAV within 4 feet of a drain source, but closer is better.  You always install an AAV  to be higher than the highest water level that the unit it is venting can reach to prevent mishaps if a clogged drain occurs.

When you open the drain fitting to dump the tank, you have a bunch of water going out a 3" fitting at a high rate of speed - that will overwhelm the typical 1.25" or 1.5" tank vent and also suck all of the water out of all of the P-traps.   I don't think  that AAV's are going to fix that, so you still need to go back and fill up all of the P-traps after you dump, usually.

Brian

[Len Silva]

Proper size vents are even more critical if you frequent rallys where they use a honey wagon to actually suck the contents of your tank.  I have seen tanks collapsed from that.

[Lin]

Our fixtures were not vented, so aside from slow draining, you could hear the gurgling from one fixture as another one drained.  I decided to try an AAV.  My plan was to pick a spot in the system that would do the job for everything.  If the first one did not work, I would add another and even another if needed.  The first one did work; no slow draining, no gurgling, not empty traps.  Unlike with electricity, where shortcuts may have invisible, dangerous consequences, the obvious performance of the fix is a good enough test.  That said, if I was building new, following the rules would be a good idea.

[steve wardwell]

when dumping we run water so as not to allow the traps to empty ...once  the massive dump is  over,, the traps remain filled and the water will just trickle out the drain we shut off the water flow then close the dumpvalve last..... thus eliminating a odorous affair and a expedited Exodus  by all partys from the offending bus........s.....

[Jriddle]

I installed three 1 1/2 vents. One for the kitchen sink , one for the shower and bathroom sink and one to vent the gray/black combo tank. I have not had any problems with smells or traps emptying. I did have to put holes in the roof but having the system work right meant more to me than the looks of my vents on the roof. I installed my tank vent in the down pipe from the toilet. I did this so when we flush the smell would not come into the bus. Seems to work better than I anticipated.

John