Toilet water gets into shower trap - help

[HellNY]

Id like to know if anyone can diagnose this problem.

Hard to believe but its true. I am a homeowner (not plumber). We recently had an entire bathroom remodel . We had a sewer gas smell coming from our new shower drain. We entertained all sorts of possibilities including inadequate venting (siphoning off the water in the trap, etc). But the vent is clear. Then I found toilet paper floated up into the shower drain. A small amount. We then did a "blue water" test by filling the toilet with clorox-blue tablets which makes the water blue. After flushing the toilet, eventually we see the blue water inside the shower drain.

This is on the 2nd floor of a single family home. I have discussed this with the plumber.

More details:

1. The celing and floors have been sheetrocked so I cant test pitch directly yet. But the shower drain (its a 2 inch) joins a sink drain and then heads north for about 8 feet, then turns abruptly east for about 18" and joins a 4-way intersection of 3 inch sewer pipe. To visualise this 4-way intersection, imagine you are standing in the center of the intersection: the shower drain comes from the west. The tub drain (separate) comes from the south, and the toilet drain comes from the east. All to one place. They all have a northward "sweep" that sends all sewage/drainwater to the north down into the sewer.

2. Added detail: when the sink drains, which is right next to the shower (its drain joins the shower drain before it heads north to the sewer intersection), the shower trap water level swells a bit and then falls back again when the sink completely drains. This implies that somehow, sink water also gets into the shower trap.


Possible explanations: The plumber swears up and down the lines are all pitched properly. He says one eighth of an inch per foot. I know he used a torpedo level when he worked but I do not know how he knows the exact slope. Yet this seems like a pitch problem to me. Or there is not ENOUGH pitch so water can flow "uphill" before it drains? Second: the toilet sends sewaged into that intersection on the exact opposite side from where the shower water enters. Although this is 4-way PVC drain pipe that is all gently "sweeped" northward, isnt it conceivable that some of the toilet water surges directly across this intersection and then, through its own momentum, carries it enough to travel the 8 feet or so to reach teh shower trap upstream? At an eighth of an inch of pitch per foot, it would have to rise up about 1 inch.

Im not a plumber but something like the above has to be happening.

The plumber suggests installing a check valve in the shower/sink drainline just before it reaches the 4-way intersection. This seems like an expedient way to solve it, but any future snaking woudl get trapped in the valve (never snake again). Should I just open the ceiling so he can do this or should I expose it all and check the entire system. Any and all input welcome.

[Basement_Lurker]

I can't really visualize your setup fully by your description, but it sounds like your 4-way fitting is a sanitary cross on it's side which leads towards a drainage stack, which would explain why you are having toilet water push into the lav/shower drain. And the piping should have been sloped 1/4" per foot, not 1/8" per foot. Your shower drain is wet vented, but you shouldn't be experiencing problems from the lav sink draining if the piping was done correctly. Who knows what this "plumber" did, but it's obvious from the problems that you describe that he didn't do things very well or understand wet venting. I seriously doubt this guy was a real plumber.

Your only bet at this point is to open the ceiling from below and see what this person did, have a real plumber come out and verify the piping, and then threaten the original guy with a lawsuit if he doesn't hire a professional to redo it properly.

[krow]

I'm suspecting that the Y for the shower drain was not rolled up enough from the horizontal plane. The slope/pitch should be 1/4" per foot. Given enough water, The toilet water can cross over the 4 way intersection allowing it to reach the shower trap at 1/8" per foot.

[HellNY]

Is teh check valve against code? If I ever had to snake the drain, I couldnt retract it and it would be stuck. It sounded good at first but now Im not so sure.

[HellNY]

I can't really visualize your setup fully by your description, but it sounds like your 4-way fitting is a sanitary cross on it's side which leads towards a drainage stack, which would explain why you are having toilet water push into the lav/shower drain. .

It is indeed a "sanitary cross." Was that the wrong fitting to use?

[Basement_Lurker]

If the "installer" did in fact use a sanitary cross on its side instead of vertically (where the two slightly sloped inlets are pointed down towards the ground), then then entire piping system should be torn out and redone properly because I doubt the slope and the wet venting was done correctly.

[nukeman]

Sounds like a mess. I take it that this job wasn't inspected? Although, some inspectors don't look at things at detail and let almost anything fly (just depends).

I would open it up and make it right. Don't try to fix it with a check valve. The problem is with the layout/slope. You certainly don't want to live with sewage coming into the shower and it would be a mess if you ever tried to sell the place. Even if the vent is clear, you still might also have venting issue along with the drainage issues. A vent does no good if it is in the wrong spot. With the other problems you are having, I would see everything he did as suspect.

Is he licensed/bonded/insured? Or is this "plumber" simply a handyman?

I would open it up and get a real plumber out there. Take lots of pics of what is there in case you need proof later. You could share the pics here and the pros can point out what else might be wrong with the layout as well.