Plumbing – Gurgling pipes after shower

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.

The drain line is probably filled with hair and soap, chemical drain cleaners at best push the clog further down and make things worse in my opinion (now toilet backing up) with the exception of “mule kick” that will eat metal pipes and I am not sure if it is even available any longer. What you need is a real snake a small one to be run down the shower, and possibly a larger power one to be run down the toilet. Without cleaning the clog this will get worse this kind of snake you hold in one hand and spin pushing it down the drain a little at a time probably less than 2 or 3 chemical treatments. You should have the land lord take care of this incase any damaged pipe or other problems come up and you are not taking the $ hit for something that should be fixed by them.