Sewer Gas Smell in downstairs half bath

[mikep-sc]

We just moved into a new home in North Myrtle Beach SC. When the bathroom door is closed, the bathroom builds up a sewer odor. I spoke with the plumber and he stated that the water tank on top of the toilet was loose causing sewer gases to enter the room. I thought the only way for sewer gases to enter the home was through a loose wax seal where the toilet meets the sewer pipe. Queston, can sewer gases enter via the water tank connection?

Thanks
Mike

[LazyPup]

It would be physically impossible for sewer gasses to even get in the tank, never mind leaking out.

[mikep-sc]

Thanks

Thanks for your quick response. Actually the plumber claims the sewer gas is entering the house where the water tank meets the toilet. There's two bolts holding the water tank to the toilet and the rubber seal was not tight. We'll see what happens.


Thanks Again.

[LazyPup]

Either your plumber just doesn't want to be bothered with the problem or his/her knowledge of the toilet bowl function is seriously lacking. In either case, I would consider consulting another plumber before authorizing any work.

I am attaching an illustration which I prepared some months ago that shows a cross sectional cutaway view of a toilet bowl.

As you can see in the illustration there is no internal passage from the drain trapway to the tank to bowl connection point. In fact, when a toilet flushes the water in the bowl rises quickly and as the water in the bowl rises it also rises at the same rate in the trapway passage. When the water reaches the top of the trapway and begins falling down the the descending portion of the trapway it creates a syphon action that sucks the remaining water out of the bowl up and over the top of trap weir. If there were a passage from the top of the trapway to the tank to bowl connection that would allow air to enter the trapway and would instantly stop the syphon action, which would then prevent the flushing action.

in order for sewer gas to leak from the tank to bowl gasket it would first need rise up from the drain, through the trapway and through the water seal at the bottom of the bowl. It would then need to rise up through the water inlet holes in the upper part of the bowl, pass through the internal water passage, then leak out through the gasket. This would be a physical impossibility because even if the sewer gasses were to bubble up through the water seal at the bottom of the bowl, once they enter the bowl they would be at atmospheric pressure. Now considering that sewer gasses are heavier than air they would either remain in the bowl or in a worst case they may be forced out through the air gaps through the toilet seat. Under no circumstances would there be sufficient pressure to force the sewer gasses to enter the tiny air inlet holes in the water supply ring, but for the sake of argument let us assume they did get into the water supply ring. The gasses would still be at atmospheric pressure, consequently there would be no pressure to force the sewer gasses to leak past the tank to bowl donut gasket.

As you stated in your original post, the wax ring at the bottom of the trapway creates an airtight & watertight seal between the top of the closet flange on the drain line and the underside of the toilet bowl. While a defective wax ring is not the only possible cause of your problem it certainly would be the most common cause.

Changing a wax ring is a fairly simple and inexpensive (typically $1 to $3) DIY repair and if you would like to attempt it I would be glad to post a complete step by step procedure to help you.

[mikep-sc]

Thanks LazyPup

Thank you for your very infomative explaination and based upon this, I will get with our plumber and have him fix the problem at the source - where the toilet meets the flange and is sealed via a wax ring.

I see your through responses to many homeowners and we all appreciate someone like you, taking the time to response to our questions.


Regards.

[Troy]

I see your through responses to many homeowners and we all appreciate someone like you, taking the time to response to our questions.

I second that!

[JCA1]

I agree, ole' Lazypup is a real hero. One of the few with enough knowledge to look down on most, but instead willingly shares and teaches others freely.