I come home and have maybe 1" of water in bottom of stem in base of bowl. This happens when neighbor flushes her toilet. I have had a plumber here, he has reset the toilet & new wax ring, gone on roof to vent from the top, routed in toilet out to sewer system to find NO blockages, he has even been over to check neighbors feed to sewer & found no blockages. He has no answers any more to help. This started 1 year ago water started being removed after neighbor flushing just a little now 1 year later all my bowl water is now gone. Neighbor has been there 8 years with no problems prior, I have no animals and the only thing that I have seen is the utilities dug up shallow wires and fixed it in the front area. Any thoughts?
I agree with Ed Beal, the plumber should actually route/snake/auger both of your vents from the roof...it seems like the neighbor's vent is clogged. There should also be vents by the street & those should be cleared as well. Either way it should be a venting clog problem, typically from crazy birds loading your first bend from the roof.
I've had a similar problem with 2 toilets connected to the same septic tank. There was no problem with the vents but water kept being sucked out of 2nd toilet. solution was to have the tank emptied, somehow negative pressure was created by the upper layer of dirt moving up and down in the tank at the level of the connection of the 2nd toilet.