3 months ago, we tiled 1 of 2 of our bathrooms, which included removing the toilet and replacing it after the tile was laid. Before we removed the toilet to do the tile, each time we flushed the toilet, it would produce a gurgle sound and sometimes the sound would come out through the sink! This is a half bath, so no tub in here. Now that we replaced the new toilet with the new wax ring, that gurgle sound has gone away totally. Our conclusion is the old home owner didn't properly seal the toilet before but now we did it properly. TWO months after we did this, we had our septic tanks pumped. Now since then, we are getting a sewer gas smell from that bathroom. Had that smell started after we replaced the toilet, we would have assumed it was how we installed the toilet, but because everything was fine for TWO full months, we have no clue what it could be and why getting our septic tanks pumped out would cause this smell. Oh, our other full bathroom has NO smell like this what so ever Suggestions?

Im not the professional plumber, but maybe you have a problem with a vent in the line - possibly a clogged or incorrectly ran vent?

Maybe the septic tank was backed up over the inlet or something and the seal was bad all along. I would duct tape over all the drains and over flows over night. If the smell doesn't go away, it is the toilet. Pull it, replace the wax ring, and reset it making sure it is solid before tightening the bolts. Use shims or floor leveler.

Sewer gas smell comes from a few things only. You have a problem with the sewer traps they are clogged so water does not stay in the trap blocking the gases from coming up the pipes or you have a vent problem. If you hear the water gurgling when you flush the toilet in the sink or tub, then that is a sure sign the vent pipe is clogged and needs to be cleaned. The sound you hear is the water in the trap of the sink and tub drain trying to draw air when the air should be drawn through the plumbing vent and not the drains. When water goes down the drain it creates a vacuum and that vacuum needs to be broken by the plumbing vent for the water to go down. Myself when it comes to clearing a vent I would get rotor reuter to come in and ream it out and certify it clear for yours and your families health.