I live in a house with a septic system. When the winter/spring rains come, the toilet on the ground level master bedroom does not flush. We have another toilet on the ground floor that does flush. We have removed the non-flushing toilet, snaked the line and even installed a newer toilet. Nothing works until the ground dries out and then it will work fine. We had the septic tank pumped out, though it does tend to fill with ground water. What I don't understand is why will the one toilet work when the other will not? Any suggestions as to what the problem might be?
Some possibilities, in no order:
The toilets vent becomes blocked somehow when it rains. Check the vents on your roof for obstructions like trees, plants, birds nests, etc.
Damaged Pipes or Tank
Water is entering your septic system when it rains though cracks in pipes, seals or the tank itself and overwhelms your leach field.
In this scenario, a backup in your house would seem likely to occur eventually. When you are having the flushing problem, check the lowest drains in your house to ensure the sewer is not backing up.
Failing Leach Field
Your leach field cannot handle the volume of fluid when the ground is wet due to rain and might need replacing.
As to why only one toilet is a problem, with the exception of the blocked vent scenario, it is hard to say. I would try flushing the working toilet over and over to see if it slows down or stops as this would help rule out that one fixture or a broader plumbing/septic problem.
Septic System?? If so, the system is FULL of water already and needs to drain out from your drain field. If it is a municipal system, tree roots CAN SWELL TO 40 % or more of their normal size in wet weather, creating a blockage- hence a slower drainage- I'd look into a rooter service if this is the case and if on a Septic System- even pumping the tank will not help as the ground water is the culprit-preventing more water to disperse. Pumping the tank will only remove liquid & solids in the inlet side- not removing water from the leach/drain field.