does this make sense? shower pan/tank connection

[handrew]

In order for the grey tank to fit we have to put it in the bay just behind the shower pan and have to connect the pan with a pipe around the frame.
We're hoping to avoid drilling through the cross member, would the attached mock up work for water flow?
My thought process is since the grey tank is below the shower pan the water will flow into the tank before the pan.

Would this ever work?

[Silver Hawk]

Just a thought - It probably will work like a 'P' trap under a sink. Good & Bad; Good: that it will probably keep a 1/2 full tank of gray water from coming up into the shower when you travel on a curvy road - which mine does (can't use the shower for storage when traveling). Bad: that it might slow down (the drop is not that great) the flow of water out of the shower.

[handrew]

that was my thought, on the 'p' trap function
will there ever be a reason water wouldn't flow into the grey tank (in terms of gravity/pressure)
would it be smart to invest in a fitting that only allows water flow in one direction?

[NJtoNC]

the hepvo (HepvO Self Sealing Waterless Waste Valve) will prevent water coming back up into the shower pan.

[handrew]

just realized my mock up didn't attach!

[MarkR]

I think your problem is going to be related to the facts that water has weight, and the law of gravity . . . I've got a friend who used one of those marine shower sump pumps and is happy with it (all things considered).

[NJtoNC]

If its vented shouldn't the water level out and seek lowest point? Why would it NOT work?

[MarkR]

the weight/volume/mass of the water in the tank will create a certain amount of pressure on the contents of that pipe. If you have a "U" shaped hose and you put water in it, it'll equal out / level on each side of the "U". If you apply pressure to one side it's going to come out the other. It can be air pressure or otherwise. If the tank didn't have sides then it would work fine . . . OR if the shower were something like 10 feet above the tank it might also work . . .

[Protagonist]

Originally Posted by MarkR

the weight/volume/mass of the water in the tank will create a certain amount of pressure on the contents of that pipe. If you have a "U" shaped hose and you put water in it, it'll equal out / level on each side of the "U". If you apply pressure to one side it's going to come out the other. It can be air pressure or otherwise. If the tank didn't have sides then it would work fine . . . OR if the shower were something like 10 feet above the tank it might also work . . .

Fluids seek their own level. The water level in the pipe will equal the water level in the tank. That means that the hydraulic head that drives the drainage is equal to the difference in elevation between the water level in the shower pan and the level in the tank. In other words, mere inches. Your shower will drain slowly. VERY slooooooowly. A check valve to prevent backflow will make it drain even more slowly.

[MarkR]

my tiny brain still wants to believe there's "head" pressure on the contents of the pipe that would push it out . . . i guess there are a couple brain cells that kind of get it. sorry for acting like i knew what i was talking about . . . kind of embarrassing.

having said that, i still wouldn't do it . . .

[Protagonist]

Originally Posted by MarkR

my tiny brain still wants to believe there's "head" pressure on the contents of the pipe that would push it out . . . i guess there are a couple brain cells that kind of get it. sorry for acting like i knew what i was talking about . . . kind of embarrassing.

No apologies needed, okay? Hydraulics are complicated; that's one reason why engineers pay so much to get a college degree. That and college is still one of the best places to pick up smart women…

"Pressure on the contents of the pipe would push it out…" only works if you don't have water pressure in the holding tank pushing back. Hydraulic head is the difference in pressure from one end of the pipe to the other. You can trick gravity to some extent by having a siphon, but for that you would need a P-trap. By the way, a siphon is exactly how a home toilet flushes; add water in the bowl until it's higher than the siphon built into the base, and then sploosh, the water is sucked out. But with just a U-shaped pipe— or in this case I guess it's a J-shaped pipe since one end is higher than the other— there's no siphon effect, just gravity flow.

[MarkR]

Originally Posted by Protagonist

"Pressure on the contents of the pipe would push it out…" only works if you don't have water pressure in the holding tank pushing back.

I guess I was "thinking" the opposite . . . that water added to the shower pan can't overcome the pressure created by a half filled holding tank . . . that somehow that holding tank body of water would pressurize the line and want to exit into the shower pan simply because it had more "mass" . . . which i'm guessing is still not true.

(and thank goodness for the siphon effect)

[NJtoNC]

the alternative is still gravity based and will likely still drain the shower pan slowly. the alternative being, cut a hole in the crossmember and drain shower into the grey tank without going below the frame. They are trying to avoid cutting into the cross member.

Which is preferable?

[TG Twinkie]

Why not raise the shower pan about 2 1/2"? Then install a "P" trap below it. Have the discharge of the "P" trap go over the cross member into the top of the GW tank with a 90 degree elbow.

[TG Twinkie]

What is your plan for venting and draining the GW tank?

[rippie]

What would happen if tank was placed directly below pan and maybe slightly offset for p trap placement or maybe hep-vo? But out of curiosity, what if it was just directly below without any trap of any sort?

[truckasaurus]

You would absolutely want a trap or Hepvo it would reek otherwise. I really like the below series of articles although it isn't directly related to your quandary. I used a Hepvo under the shower pan which was elevated on a frame about 3" tall, this allowed me to route the post Hepvo plumbing over the frame and down into the tank.

Water, Water, Everywhere!

[robwok]

I don't think the frame member is solid. Have you looked at it? Maybe it is in that era. I don't think you want that trap extending below your trailer. You'll have issues with freezing possibly, or getting knocked around maybe.

Even if your frame is solid, I would recommend a couple things:

1. cut a hole and weld a ring of steel to support the floor and the rail on both sides.
2. Cut a cole and bolt plates on both sides. Get flat steel about 2 feet long that will fit on either side of the cross member. Drill hole through that, place bolts 3 on each side of the hole to bind it, zig zag pattern.

Run the drain line through that. Get a P trap in there to assist with gasses and with the sucking action to drain your shower.

Don't do this with the frame rails, just the cross members.

[NJtoNC]

the crossmembers aren't solid. they are 'c' channel. truckasarus, you don't have a problem draining your shower pan using the hepvo? The the other issue is that this is a 53. our friend, The OP, is very tall and as it is he can barely stand up in the trailer. he's already got to 'hunch'. raising the shower pan is not out of the question, but it is still located overtop of the bay next to the grey tank; the shower pan is over the axle and grey tanks are fore and aft of the axle.

Excuse the rough sketch:

something like this would raise the shower pan enough to run the lines OVER the frame but would make it impossible for ansrew, a future full timer, to stand and shower.

[TG Twinkie]

Even with a "P" trap. It would not extend below the frame rail and would be above the belly pan.
Not sure how the "H" valve works, but there are no moving parts in a "P" trap.