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Unique unsolvable drain issue

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Razzle1980

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I've been dealing with the same drain issue for over a year now. It started about a year after we did major construction, which included all new ABS drainage piping in our slab concrete foundation (main drain is 4").

Our master bathroom shower, which is a step down shower and the furthest point in the house from the street (1-story house), has a periodic smell coming from the drain. There's water in the p-trap, but the water itself reeks of rotten eggs from time to time. I've siphoned the water and smelled it, so I can confirm the water is somehow getting contaminated. I've done a coliform bacteria test and hydrogen sulfide test, which have both been negative. Weeks might go by where it doesn't smell, and then it will all of a sudden come back, day after day no matter how many times the shower is used. I can't figure out what the problem is not can multiple plumbers I've had come take a look at it, including the plumbers who installed everything. I have a tankless water heater and no water backup issues.

One of the plumbers pointed out that my setup was odd, because next to the step down shower, I have a toilet which is higher in elevation. He though there might be an issue with that connection, which is what prompted me to do a coliform bacteria test on the smelly water in the p-trap, which was negative.

Any thoughts? I'm considering possibly pursuing legal action against my contractor who has given up on exploring solutions because I'm all out of options.
 
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arctic bill

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Many years ago i had the same problem. what i found that there was a slight counter slope so that sewage would back fill the trap . I would redo the piping so that the shower is connected well above the toilet both in slope and connection .
 

Razzle1980

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Thanks for your reply. If there was a counter slope, wouldn't it be obvious every time I flushed the toilet? Wouldn't water back into the p-trap and raise the trap's water level? I also assume if sewage was backing into the trap, my coliform bacteria test would yield a positive result? Redoing the connection is a last resort option, as it means demolishing new tile and concrete
 

Jeff Handy

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As a cheap and dirty fix, just cover the shower drain with a wide flexible rubber tub drain cover, commonly available in hardware stores or on Amazon.
Remove it during a shower.
 

Razzle1980

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20201023_165513.jpgThe drain has a grill on it, so I can't just cover it with ease. I do have one of those one-way plugs, but I'm looking to find the problem and permanently resolve it, given that a lot of money was spent less than 2 years ago on this.
 

Jeff Handy

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You say you don’t wan’t to tear anything up, but yet you want a miracle solution to an unsolvable problem.
Get the plumbers back who did the original work.
If he won’t keep helping, you have to be creative on your own, or bring in lawyers.
 

Jeff Handy

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Have the bathroom drains all been snaked?
Out to the main line?

Have you tried adding an enzyme drain cleaner like Drain Defense from Zep, to all the bathroom drains, on a weekly basis?

It slowly and safely removes build up in the pipes.

Have another coliform test done somewhere else.
Clean water does not stink.
 

Razzle1980

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I'm not saying I don't want to dig things up, just saying that would be a last resort solution. I figured I'd post the issue here to see if it might spark a possible cause and/or solution to the problem. That's all.
 

Jeff Handy

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You might have lack of proper slope on a drain line somewhere, which leads to build up.
Snaking, water jetting, or maybe just Drain Defense might solve the issue, without any demo.
 

Razzle1980

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Thanks Jeff. I've tried those solutions. If I had a slope issue, wouldn't I have a backup somewhere eventually? Ive never had a backup anywhere.
 

Jeff Handy

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You can have a partial backup, caused by the bottom of the drain having build up, and not allowing full flow.
So the line will gradually hold more and more water, but will still keep draining.
Your shower is the lowest fixture, so some water is backing up into there.
Not enough yet to emerge from the trap up into the shower pan.

Have you had all the lines camera inspected?

That would show any buildup or standing water.

You can also run water with the camera in there, to observe sluggish draining.

Anyway, happy hunting, hope you figure it out!
 

Mark.S

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Dunno if this helps at all but both in my present house and the one before we had intermittent smell from our shower floor drain. Neither house had any drainage issues and as far as I know all piping is per code. Houses built circa 1980.
My wife is v sensitive to this and she says it seems to happen in warmer weather and she is convinced it’s just remaining shower water that sits in the trap for a few hours and creates the smell. It’s not overpowering but just enough of a yuk factor to be noticeable.
We just flush the drain with clean water and spray bleach which seems to improve the situation.
Not sure of the diameter of your drain immediately below the grate but depending on the volume of water sitting in there and whether it’s 100% clean or has some stale shower water or residue it could be a factor.
That’s my 2c. Hope it’s helpful...
Other than that I agree with Jeff’s suggestions and taking more samples if you’re really concerned about possible toilet water getting in there
 

Rickyman

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Use a shop vac and remove water from trap. Flush toilets and run sinks. If there’s still no water in the trap it’s not draining backwards
 

Razzle1980

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That's actually a fantastic idea...can't believe I didn't think of it myself. I'll empty the p-trap water and check back 24-48 hours later to see if there's any water in there and report my findings here. Thanks to everyone for their recommendation.
 

Jeff Handy

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Be aware, while the trap is emptied, sewer gas can be released.
You might want to lay some wet rags over the tub drain to keep the stink from escaping.
 
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