We just recently purchased a home that has a finished basement. The full bath downstairs has a sump pump to send the sewage to the septic system. There are two things happening and I can not figure them out. I believe they may be related:

1) When we flush the toilet downstairs, it flushes pretty well and the water is flowing to the septic. You can hear it go through the line (do not ever hear the pump). After you flush it, you start to smell sewage in the garage near the pump, and worse in the basement (septic line runs above drop down ceiling) and closet (where the line goes to septic). It does not smell in bathroom. This is the only time it smells. This line connects to the main sewage line. Why does it smell? There are no leaks. The sewage vent goes to the attic where it makes a right turn and connects to original sewage vent.

2) At random times through the night, we here this knocking sound. We have concluded that it is the water line. It does not do it when anything is running. It does it mostly at night when things are off. I have shut off valves and when I shut off the basement bathroom water supply, it has not happened for two nights. The knocking sounds like it has a restricted flow, but it has a distinctive pattern. Does the sump pump require water from the main line? The knocking takes about 20-30 seconds when it occurs. I have yet to notice the toilet running when it makes the noise, but I have not checked since it has not happened since we shut off the water.

Any help would be great!!

Thanks

Chris