We just moved into my mother in laws house, and had some problems with the septic tank. There is an apartment above the garage as well, so there is a total of 3 bathrooms, and two families doing laundry, which is a lot of laundry, and dishes, and showering. Anyway, the toilet in the house would overflow on occasion, and water would back up into the bathtub of the downstairs bathroom. We eventually found out that the septic tank was full, and had it pumped. This was around the end of January beginning of February, and it is a 1300 gallon tank. It is now only June, and again the toilet has overflowed, and water is backing up in the tub. If I try to do laundry, I can hear the water bubbling in the sink. It isn't possible that the septic tank could be full again in just 4 1/2 months, so what could be causing this to happen again?