Frame rails as drain traps?

[Iceni John]

OK, that's got your attention!   I expect you're wondering "Eh?"

My bus, unlike most on this forum, has full-length frame rails.   In order for the drain pipes from the shower, kitchen sink and bathroom basin to reach the gray tank's inlet, all three have to duck under the frame rails, then rise slightly before connecting into the tank's inlet pipe.   In other words, they will drop, then rise a few inches on the other side of the frame rails, just like normal traps do (but they are in a more compact form).   Is there any reason I could not use these de-facto "traps" under the frame rails instead of normal U-shaped traps?   After all, they'll do the same thing  -  they'll keep a small amount of water inside the pipes to prevent gray tank odors from reaching the bus's interior.

I know NFPA 1192 pontificates on everything and anything, including drainage matters, but I don't see what relevence a Fire Prevention code has with waste water drains!   I'll definitely follow 1192 when it comes to propane and electrical installations, but for drains and gray tanks, nah.

So, all you plumbing experts and cognoscenti of drains, do you think I can do this without stinking out my whole bus?

Many thanks, John

[mikelcan]

One thing that can happen if there is too much vertical distance from the drain to the trap is the force of the falling water will create a vacuum on the back side and pull the water out of the trap.  I am not sure of the actual layout of your bus so I can not speculate if that will happen in your situation or not. 

Mike

[bevans6]

They won't act as traps properly, but what they will do is act as restrictions that will prevent proper water flow and drainage into the tanks.  Any and all solid/semi-solid or viscous waste will collect there.  I would find another way to get the water to the tank that is constantly falling, not down then up again.

Brian

[crown]

 john i had a proublum like yours i hade the frame outriggings in my way what i did after lots of
thought was to cut a 3'' hole in frame then weld a 3'' 1/4 thick pipe in hole and plate it .now drain
pipe goes through the new pipe / hole. hope this helps john
ps this is fully welded and steel plateed /boxed i am sure its stonger then before

[joel_newton]

I also have frame rails and am facing the same challenge.  My gray water tank will be behind the rear axle between the rails.  The longest drain line run is about 13 feet from the shower and will be between the rails. I am exploring two options for gaining the necessary fall.  With an 89" ceiling height, the floor tentatively will be 2x4s on edge sandwiched between plywood.  Per 1182 p31 this 13 foot run is legal with two hubs with 2x4 in the floor.  A second option - in an initial analysis of the frame, I found that a 1 1/4 pipe will almost fit between the frame rail and cross member.  A short section of pvc could be heated and squeezed in.  One end would be connected with transition glue the deformed end with a threadless hub.  Two 45s would be used to drop below the bottom plywood flooring.  This would provide for plenty of fall in the drain line.  I'll probably use a combination of the two.

Good luck.  Let us know what you do.

[Geoff]

I had a similar problem with my RTS conversion but it was the bulkheads and partial frame that was in the way of draining the shower and sinks directly into the grey tank. So I used a marine shower sump pump.  Works great, but is not for camping in below freezing temperatures.  I did a quick Google search and found one:

http://www.iboats.com/Attwood-Shower-Sump-System/dm/cart_id.216851528--session_id.734892075--view_id.37909

--Geoff

[Jeremy]

....So I used a marine shower sump pump....

Those things are widely available for houses too, for when people install bathrooms in cellars and so on. They were my first thought too - not being overly comfortable on plumbing issues I wouldn't be inclined to experiment with the home-made U-bend ('drain trap') idea myself. The sump pump may be overkill, but I'd probably rather buy one of those than contemplate cutting holes through the chassis rails, if that was the only other solution.

My bus has a full chassis as well of course, but fortunately it is directly below the floor and above the bays, so the same problem doesn't occur

Jeremy

[Iceni John]

Thanks for your answers.   Holes through frame rails are not going to happen!   A sump pump, or three of them, would work, but that flies in the face of my KISS design criteria.   I've just thought of a possible long-shot third option  -  my floors are 1-1/2" insulated marine plywood, laid directly over the frame rails and understructure.   It may be possible, just, maybe, to run 1-1/4" thin-wall drain pipe through the floor, but parallel to the floor, almost like how PEX tubing is inset into the floor for heating.   If, and it's a big if, I can excavate suitable channels in the floor to fit the three drain pipes, I could then get them from above and outboard the frame rails to above and inboard the frame rails, then it's a straight shot down to the gray tank's inlet.   Basically I've got 1-1/2" of space to make this happen, without them protruding above floor level.   When I go to the bus tonight for my usual fossicking and fettling I'll measure everything and see if this hare-brained idea is doable.   Mind you, converting a bus in the first place is a hare-brained idea anyway!

Thanks, John

[Sean]

...   In other words, they will drop, then rise a few inches on the other side of the frame rails, just like normal traps do (but they are in a more compact form).   Is there any reason I could not use these de-facto "traps" under the frame rails instead of normal U-shaped traps? 

Yes, and some of the reasons have already been outlined.  There are very good reasons why plumbing codes (including 1192, but also the UPC, etc.) stipulate that traps need to be within a certain distance of the served fixture, how much vertical drop is allowed, etc.  Also note that each fixture needs to be vented, and there is a strict limit on how far the vent can be from the trap -- I can't see, with the way you described this arrangement, how you would properly vent these "traps."

...
I know NFPA 1192 pontificates on everything and anything, including drainage matters, but I don't see what relevence a Fire Prevention code has with waste water drains!   I'll definitely follow 1192 when it comes to propane and electrical installations, but for drains and gray tanks, nah.

First, understand that NFPA did not develop the plumbing sections of this code; they simply inherited stewardship of it from ANSI (when it was ANSI 11.92).  And most of the plumbing provisions were adapted from the relevant plumbing codes.  It just became too confusing and cumbersome to have three different organizations involved in the updating of a single code standard, and NFPA ended up with it by mutual agreement.

Also understand that improper waste-water plumbing can kill you just as dead as improper wiring or propane installation (yes, it has happened).  More likely, it will just make you ill, but why put yourself or your family at risk?  Follow the code -- absolutely every provision in these codes ultimately came about because someone was harmed.

I can pretty much guarantee that if you proceed as you have suggested, you will get sewer gas in your coach, and you will get solids buildup in the pipes.

There are lots of ways around this kind of problem.  You can run some of the DWV plumbing above the floor line, in cabinets and toe-kicks.  You can use tanks that are shallower but longer or wider, or multiple shallower tanks connected together.  You can use multiple tanks and use a sump pump, as already suggested, to transfer waste (although this presents its own set of complications).  Or you can have your waste line enter the tank from the side instead of the top (although this requires a separate tank vent, as opposed to the normal wet-vented system).

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

... It may be possible, just, maybe, to run 1-1/4" thin-wall drain pipe

Careful here -- not all thin pipes are suitable for DWV.  You'll want Schedule 30 DWV pipe with listed DWV fittings.

through the floor, but parallel to the floor,

Drain fittings need to be continuously sloped to the tank.  So "parallel to the floor" will only work if the floor itself is sloped in that direction.  If the pipe is not sloped, you will get buildup, which is one reason why the code specifies a minimum slope.

.. If, and it's a big if, I can excavate suitable channels in the floor to fit the three drain pipes,

This one has me confused.  If you have three fixtures on one side of the bus that need to drain to a tank on the other, why use three separate drains?  Without seeing your drawings, it's hard to make concrete recommendations, but I would simplify this problem by using proper DWV wye fittings and combining the outflow from these fixtures into a single drain.  Combine the vents with vent tees so you need only a single hole in that side of the roof for the vent.  If you use the proper size drain, with only three fixtures you can wet-vent and use this same vent for your tank.  I am guessing running a single 2" drain will be easier than three 1.5" ones ...

I could then get them from above and outboard the frame rails to above and inboard the frame rails, then it's a straight shot down to the gray tank's inlet.   Basically I've got 1-1/2" of space to make this happen, without them protruding above floor level.

If that's all you can fit, you probably can't do it, because I am guessing that the shower will require a 1.5" drain, which will make the OD larger than 1.5".  The sinks might have 1.25" drains.

Also, with this arrangement, how will you run the trap for the shower?  Is the shower drain located above floor level?

If you can post a sketch of your layout perhaps I or someone else here can make some more substantive suggestions.

-Sean
http://OurOdyssey.BlogSpot.com

[crown]

 just to clear things up i did not cut a hole . in my main frame rails that run front to back.
i cut one hole 2'' and had it welded by a pro in the small outside frame rail the one that
comes off the frame and goes out to the side of bus. what i did i was told was overkill
as to making it super strong  john    ps. it was for my shower drain

[garhawk]

If all the other advice has not convinced you to NOT use the rails as traps, consider that the acids from sewage will exponentially eat away at the metal.

[Iceni John]

Thanks again for all your good advice for a plumbing newbie like me, especially Sean and his wealth of minutiae.   Some things are now clear:
  1.   Individual traps are still needed, regardless of how the drains are run from that point on.
  2.   Each drain must be adequately vented.   I've been reading about AAVs, which sound better than making more holes through my roof.   Still, more research needed here.
  3.   I've not completely given up on the idea of running my drains under my frame rails, but they will have to rise as minimally as possible after they clear the lower flanges.   With this in mind, I'm going to make a simple experimental rig using clear plastic tubing that I can configure to simulate different scenarios and geometries, and run water through it at different rates and volumes to see exactly what happens.   I'm thinking of adding some fine sand to the water to see if it accumulates in the lowest point, or if the flow will move it through.   If it works OK, great.   If it doesn't, at least I've tried and seen what actually happens, without making everything for real in the bus, and a few feet of tubing is cheap enough to play with.
  4.   I checked the Running-Pipes-Through-The-Floor idea, and it won't work.   I've got some hefty seat rails (welded onto the frame rails) that are inset below the floor, so they prevent me running anything there.   Too bad.   I'm not cutting away those seat rails because I'll be later bolting all my interior walls and cabinets to them.
  5.   Yes, it would be nice to have the gray tank elsewhere, directly under the sink and kitchen on the right side, but I ain't got no more elsewheres!   Literally every inch of space underneath is being used for one thing or another, and the house batteries must go under the shower and kitchen.   The gray tank is slung under the frame rails, just like the fuel tank, between the rear of the belly bin and the differential.   The frame rails are 8" high and 3" wide mega-tough steel (it's a Crown!), so nothing's going through them!   The loo is on the left side, but it drops straight into the poo tank  -  that one's easy.
  6.   Just to complicate things further (!), I'm thinking of having my shower set about 4" down, to give me more head-lathering room inside it.   Because the actual floor is 1-1/2" thick, it will protrude only 2-1/2" below the bottom of the floor, but it will make the vertical distance less from its trap to the gray tank.   I hope the few remaining vertical inches from the shower to the gray tank will suffice for good flow.   We'll see.
  7.   Yes, I'll try to combine the shower's and kitchen's drains into one.   Good idea, thanks.
  8.   Now I know why NFPA 1192 talks about poo tanks and other things not usually considered to be major fire risks.   Talking of methane, I bought a short piece of polished stainless pipe for my black tank's roof vent, and the PVC or ABS vent pipe inside from the tank will connect to it.   I'll be the only busnut with a gangsta' bling poo tank vent.   Maybe some diamonds on it would look good?   Would that make it Crap Rap?

Thanks again, John

[Iceni John]

Oops, misfire

[crown]

 john why not put your batterys under the drivers seat thats a huge unused space you would need to make a door no big deal then you can put your gray tank under your shower .
john proud owner of a 57 crown