2 or three years ago we noticed very localized drywall damage in a kitchen soffit below the upstairs tub / toilet. Turns out the wax ring was leaking (looks like the wax rig never made full contact, possibly original back to '71 construction). I installed a thicker wax ring with the integral plastic funnel. After that the adjacent tub drain would gurgle when flushing the toilet (not always but about 90% of the time). Thinking that the problen was a blocked vent pipe, I went on the roof and using a drill motor sized portable drain auger, angered 20+ ft down the vent stack. Nothing was snagged in the auger tip when retracted, auger motor never labored and no change to the gurgling frequency.
Lately it does not gurgle quite as often - maybe 50% of the time. I am about to replace the original '71 avocado green toilet with a 1.6 gal Champ 4. What should I be looking into with respect to cleaning drain and vent while I have the toilet removed? What is the possibility that there is an obstruction between the toilet drain and the vent stack?
I searched for gurgling toilet on this forum and read half a dozen questions & replys and several of them mentioned possible down stream blockage. I had not considered this - there is no back up in the tub when flushing the toilet nor does the toilet flush slowly. House was built in '71 and has cast iron pipes with band clamps at the joints. House has a basement. Any recommended diagnostics I could/should do prior to removing the toilet?
In addition to the small 5/16 dia cable drill motor/drum auger, I have an Electric Eel drain auger (with sectional cables). I have never considered taking it inside of a living space and I am guessing if I were to use it, I would need to work at guiding / restraining the cable while my wife turned the machine to minimize the risk of having it flop around.
Sounds like either your bathroom drain may be partially blocked downstream of it's vent so when the toilet flushes it's pulling the trap on the tub. Or the idiot that plumbed your house did not bother venting that fixture...