Three months ago when we moved into our home, the toilet started gurgling so we had septic tank pumped, and drainline from house to septic cleaned out. Two months ago, happened again, so we tried a chemical clog remover that helped for a bit. Last week, it started again whenever water was run. Plumber came out and cleaned a clog out of vent line which is now completely clear, and installed a secondary vent (he can't figure out where the vent connects with the line). Gurgling now only happens when a lot of water is released into main line, such as after a load of laundry is washed or a sink of dishes is drained; air is bubbling up into the toilet, and it seems to get faster as the amount of water in the pipe decreases. The drains are draining normally (no slow or delayed draining) and there is no standing water in the outside check pipe between the house and septic tank. There are no trees or plants anywhere around the drain lines out of the house or from the tank to the drain field. Help!! I literally have tried everything and have NO IDEA what else to do!! Thanks to everyone who has been trying to help me diagnose this!!
If there is not any backup evident at the outdoor clean-outs or tub drain when sinks and toilets are flushed together, then I would say the septic is not slow draining and air bubbling into the toilet requires that the soil vent serving the toilet be plugged some other way. Since the toilet vent line was recently cleaned and found to be plugged, I would surmise that the vent has somehow become plugged again.
Offhand I can think of two possibilities:
(1) The toilet soil pipe has a sag near the connection to the soil vent such that the branch to the vent tends to collect sewage and become plugged;
(2) The toilet soil vent is connected to the drain line incorrectly (incorrect wye, installed backward, etc);
There are companies for hire that can run a camera through the lines to find the problem if you are so inclined.