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Question DetailsAsked on 8/21/2017

Our newly constructed home's guest bathroom toilet plugs up on occasion. No amount of plunging makes it go down,

If we wait an hour or so, the water goes down by itself and normal flushing is OK until the next time. During the hour wait, the bathtub drain gurgles and bubbles come up in the toilet bowl. We have no issues with the master bath toilet, just the guest bath toilet. Both bathrooms have separate roof vents. We have had warranty service come out, however, they cannot duplicate the issue when they are here. Is there something they should look for other than flush the toilet several times, indicate there is nothing wrong, then leave? Is there a plumber you could recommend? Our mailing zip code is 34748.

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1 Answer


If bubbles are coming up during the hour wait (not just when flushing) that sounds like something other than just a normal partial blockage in the line downstream of the bathroom - because in that case you can get bubbles while the flushing is going down the drain, but not for a long time thereafter.

My guess would be either a downstream vent connection is plugged up by the flushed water (causing sewer gases to come up in the tub and toilet) which would imply incorrect venting piping - or none at all. Could also be caused by a SIGNIFICANT sag in the swer pipe acting as a trap. Here is a related article on that -

Another possibility - falling in the incorrect venting category though - is a very common plumbing mistake I see - bathroom plumbing generally like this with soem omissions -

You can see the various fixture commections (obviously closer together than normal) with the vent stack to the right, and vent stubouts up from each fixture. Some plumbers are improperly doing what was common in the 30's and 40's and into the 50's - skipping the individual fixture vents (the 90 degree stickups from each fixture location) and counting on just the tail end vent stack (flow is from right to left in this mockup, into the 4" main stack pipe at far left). Sometimes it is plumbed like you see here, sometimes on a straight-through DWV branch with each fixture dropping pretty much right into it - but you can see the vent pipe is horizontal and at the same level as the branch below the toilet rather than coming from above - this promote backflow of solids into the horizontal run of the vent pipe and rapid clogging - meaning, without any individual vent connections from the fixtures, the outgoing vent cannot accept and vent the air from in the drain lines as they fill with water if there is any restriction, or leet in makeup air to prevent partial vacuum from forming in the pipes as the liquid flows down the pipes.

As the referenced blog says, when you put a large amount of water into the drain line (flushing, draining full tub, washing maching emptying) it displaces air in the line - some moves ahead of it down the pipe to the street (especially if flowing as a pretty much solid plug. Some of the sewer gases, if the flow is not "plug" flow but only partly filling the pipe,expands to wherever the least resistance is - a nearby trap if no open vent is available, otherwise up the vent pipe to the roof. Also, if partial plugging or plug flow (pipe running full), then if there is not inflow air from the vent behind it, it pulls a partial vacuum and the water drains goes down very slow - sounds like your case, huh ?

Because this is going for an hour, I would guess you are getting sewer gas from the septic tank or sewer as well - coming back up the sewer pipe, and not being able to escape through the vent stack is pushing up through the water in the traps.

One other thought - if on septic, here is a good article on inlet pipe plugging in the tank - a pretty common thing, either from toilet paper matting or from floatable getting stuck in the outlet - this can cause both partial backup and issues with gas venting from the tank if its air vent is blocked or frosted up.

I would say the solution is to have a sewer camera run through the vent pipe into the bathroom pipes, and also from the bathrooms pipes (commonly by removing the toilet to access the larger DWV line, but sometimes from under a sink by removing the trap) to look at the entire DWV piping in the bathroom nd from theereon out to the septic tank or street sewer main - looking for incorrect piping, blocked vent pipe, sags in the piping cuasing a trap situation, etc. And I would say the builder should be paying for it - at least if something wrong is found for certain. Some sewer and drain cleaning outfits have the capability of recording the camera run on DVD or thumb drive so you could show the builder- of have him have a rep there during the run to see what the camera is showing.

You can also photo the flushing and subsequent tub and toilet bubbling as proof you have a problem.


One other after-thought - is the guest bathroom at lower elevation or located "downstream" of the master one in the plumbing arrangement ? If so, could be you just have a normal partial clog in the sewer line downstream of the guest bathroom, causing air to bubble up in the nearest traps (still because the vents are not working right or not done right) as the liquid fills the pipe upstream of the clog, pushing the air back up the pipe. if this is the case, I would guess the bubbling would be worst when washer is emptying (assuming it is connected in upstream of the blockage), and if the master bath is "upstream" of the guest bath I would guess flushing there also causes the bubbling in the guest bathroom.

Answered 3 years ago by LCD

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