Toilets, Sinks, Showers, Tubs and Disposals - toilet leaking gas, please help

okay, so here's the problem. since replacing an old toilet in our condo, there is a persistant sewer gas smell and every few minutes you can actually here "sssssss", like someone slowly letting air out of a balloon, lasts about 4-5 seconds, stop and repeats. i've replaced the wax seal 3 times now using a single ring, double rings and a single ring with the black liner insert. each time, i've been absolutly sure to lower the toilet straight down and with tape markers from a dry fit as guides. i've not wiggled or moved the toilet as i bolted it down and have used a level to make sure everything is true. there is no water leaking, just gas.

I'm now very frustrated and ready to throw the bloody thing over the balcony, cement the damn hole and start using a bucket.

Any help would be VERY much appreciated.
Thanks in advance.
W.

I would check the vent pipe, it should allow the gas to be vented out. Sounds kind of funny to have that much gas built up in your sewer pipes....enough to cause pressure to push past the wax ring!?!?!?!?

That is why you have water in the toilet to prevent the gas from coming up in it. So if the gas is leaking past the wax ring, but not blowing bubbles in the toilet, your vent is not working properly. The vent should be a straight shot to the outside, with no obstruction/resistance.

What you are describing as a hiss, may be water flowing back into the toilet tank. If you valve off the water supply to the toilet, does the hiss stop?

If so, the toilet flapper is not seating properly and water is slowly leaking out of the toilet tank...........the float is dropping........and the fill valve is opening to add more water to the toilet tank.

Try valving off the water supply to the toilet and let us know if the "hissing" stops.