fourth year
Probably not, but check it to see. Have someone flush the toilet while you listen at the vent on the roof. If you hear the toilet flush you do not have a blocked vent. You more than likely have a situation where your septic system is flooding due to the rain satuating the ground and your pipe into the house is filling with water possibly right up to the point where the lowest toilet will not flush properly. Then when the ground water recedes, it takes the water in the lowest toilet with it.
