That’s what I’m experiencing in the upstairs bathroom, and not for the reason you might expect! Anyone with any plumbing knowledge, there is a foul, foul odor permeating the room, I think the wax seal holding the throne in place might be disintegrating, or some plumbing is backed up somewhere. (The potty occasionally flushes itself in a ghostly manner.) I suppose I’ll have to have a plumber in, but I’m curious as to what might be causing this hideous stench, and if it is going to cost an arm and leg to fix it. Anyone?
It could be a dry trap. The trap is there to keep a water seal between the main drain and the outside. Try pouring water into any drains, particularly if you have a floor drain. This can also be caused by the vent being clogged. Animals or vegetable matter (leaves?) may have clogged the vent.
In any case, this is not only an annoying situation, but could be unhealthful. It could also be dangerous, as sewer gas is highly flammable.
Get a professional in there ASAP, and open a window until then.
Sounds like you’ve made a pretty good diagnosis. Yes, I would expect it to be around $200 or so. That’s just a guess but it depends on how old and how difficult it is to remove the toilet, remove the old ring, replace it and then reinstall the toilet. You could be looking at maybe a couple hours of work, tops?? That’s my semi-educated guess. Hopefully I’m wrong and it will be less! good luck!
Either of the previous posts would be a possibility. You mention that the toilet flushes by itself, so the trap would have water in it, and there likely wouldn’t be a clog. A bad seal would cause sewer gas to leak in from the waste stack. If it’s a 2nd floor bathroom, have you noticed any staining or signs of leakage on the ceiling below?
If it’s an old house, or if you have no idea when or if the wax gasket was last replaced, you’d probably be better off changing that. If the flush valve assembly is leaking or flushing itself, you should change that as well, plus the flapper. If you’ve got an old valve with a float ball, you can get a complete repair kit (valve and flapper) from Fluidmaster (if you’re in the US) at any Home Depot, Lowes, etc. I believe it’s a Fluidmaster 400. It’s not too difficult to replace if you’re fairly handy.
Changing wax rings aren’t too bad, except for getting the old floor bolts off. Usually they are corroded, and can be a bitch to get off. If you’ve never replaced a bowl, you’ll need a helper to get the new one in place properly. And of course, get all of the water out of the tank and bowl (use rags) before removing anything. While the bowl is off, it’s a good idea to plug the 4" opening - as danalan said, methane is flammable. Plus you already know it smells like shit.
Whether you do it yourself or hire a plumber, you might just want to get a whole new tank/bowl combo. You can get a modest set for under $100, a new wax ring would be about $5. Plumbing labor would likely be at least equal to or double material cost.
Well, now the smell seems to be gone! The other day it was so bad that even Mr. Salinqmind noticed. Which is saying something. Anyway, he says he knows how to replace the wax seal, so I hope that’s what it is. Thanks for the info.