I have a house that used to be on a septic system, converted to city sewer. The old septic tank still receives waste from the basement drains and toilet. There is no kind of vent anywhere on the sewer lines. Most times the toilet and all drains work fine with the exception of an occasional gurgle. But when it rains really hard the toilet bubbles VIOLENTLY and then sucks the trap mostly dry.
A plumber used a camera on the drain and said it is fine and suggested some interior drain vents with check valves. Could this fix the problem and why does it act up when it is raining hard?
I should have included that the contents of the septic/holding tank is pumped up into the new city sewer pipe.