What is causing a periodic REALLY bad smell from a bathroom?

Question

I live in a house with a bathroom downstairs in the basement, no window, only a powered fan/vent. Periodically, say once or twice a day, there is a terrible sewer like smell coming from the bathroom. Not connected to any specific use as I can tell, nor can I tell whether the smell is coming from the sink, shower or toilet specifically. I think they are all on the same drain since when you flush the toilet you can hear it in the shower drain, same with the sink. Neither the shower nor the sink run slowly so I don't think the problem is a clog. Any suggestions on what the problem is/how to fix it would be great since the smell gets pretty strong.

Answer 1

Of course all the drains are tied together. the sink has it's own trap, and so does the shower and the toilet, but then they're tied together and also tied to all the sewer lines in the rest of the house.

The stink is may be coming from a toilet not sealing properly. The toilet has it's own trap built into it. If the wax sealing ring under it is compressed or if the toilet is loose it would be letting sewer gas past it. Stick your face, you nose, down as close to where the toilet meets the floor and see, ..er, smell if it's strongest there.  If it is, remove the toilet and reseat it with a new wax ring, or have a plumber do it for you.

Answer 2

Your bad smell is sewer gas.  It can come from a variety of places.  The bad seal on the toilet, is exactly one of the sources.  Other sources can be the drains themselves.  If one of the traps has a leak, when it leaks down past the bottom of the neck, the gas comes in.  Also, since you said you are in a basement, there are two other items to look for.  Do you have a sewer pump to raise your drain water to grade?  If so, the seals on the top of this pump may be bad.  Also, if the house is older than 20 years, check for a floor drain, that may have a dry trap, or a trap that is only getting wet when you use one of the other fixtures.  

Since you said you could hear water in the drain of the shower when you flush the toilet, check that trap first, to make sure it is staying wet.  

Last, if all your traps are holding water, and the toilet seal is good, and there is no floor drain or sewer pump,,,,, if you are on public sewer are you at the bottom of hill.  Water and sewer flowing to the bottom of the hill can create low amounts of pressure in the system that can bubble through your traps.  If this is the case, you need to invest in a back flow preventer, installed in the yard, at the sewer connection.  

(((Last thought,,,, get some rubber drain stoppers to put into your drains, and the flat kind to go over your shower drain to give you some releif until you track down the problem.  You will also have to plug the overflow drain on the sink. Remember, sewer gas not only stinks, but it is a hazardous gas, containing any number of constituants such as methane or even hydrogen sulfide.))))

Answer 3

the seal in the p-trap in your sink may be out. it allows sewer gases to get into the potable water system. honestly i dont know how this happens but im new in home inspection and i know this can happen.

Answer 4

Put bleach in the toilet, let it sit for 10 minutes then flush. Also get those bleach tabs that you slip in the tank of the toilet. Try that before you hire a plumber. If it's not a toilet that you use every day, make sure you flush it once a day. Hope this simple fix works.

Answer 5

Do you have a septic tank or a sewer system in the house? If it is a septic tank, then it could be that it is almost full and might be time to get it pumped out.

Either way, something that may help is an enzyme based septic system cleaner, which should help clear out anything that is causing the smell.

Hope this helps!

Answer 6

Some of these answers are very good.  One thing not mentioned is the vents.  If they are undersized, or partially blocked,  it is possible that when you flush the toilet, it is causing the drains to be sucked dry, thus causing the smell.  This would explain why you can hear the water in the sink or tub, when you flush the toilet.  A combustible gas leak detector, could be used to pinpoint the location of the leak, although, if it is a small confined area, you might get false readings, if you don't know how to use the detector. good luck!  P.S.  Don't put any type of bleach tabs or cleaners in your toilet tank.  They will prematurely breakdown the flapper or any rubber seals.

Answer 7

If you flush the toilet and can hear it in the shower, that tells me only 1 thing. The sewer vent is your problem. The toilet is probably the culprit because it uses alot of water all at once sucking the water from the trap in the shower or sink and thus the sewer smell. Basement bathrooms are notorious for never including the necessary sewer vent which allows the toilet to suck air instead of the water in the traps. If the proper vent pipe is there it must be plugged.

Because your bathroom is in the basement, you probably won't be able to see any drain pipes to know if they exist or are plugged.

Best advise is to call a plummer to install the proper venting or clean out the existing vent. Yes I know it's going to be expensive. Other option is to make sure the traps don't get sucked dry. The sink is easy by installing a drum trap, but the shower is not so easy because you probably do not have access to the drain, so make sure to run the shower for a few seconds after flushing the toilet.