Question
BACKGROUND: We have a septic system. Sewage was flowing out into the yard. The clean out was found to have the cap missing, which was replaced. Once the cap was replaced, the sewage began to back up in the house. When we would wash dishes, sewage would bubble up into the bathtub, the toilet would not go down, the bathroom sink would drain slow and gurgle. First plumber ran snake, said it was not clogged by us, but that the piping was laid wrong. Next plumber dug up where piping runs to septic tank, said there was grease clogging, also another fitting (? I don't really know proper terminology) was broke off--so said it wasn't draining right.
QUESTION: How long would it take for grease to clog system enough to back it up? We have lived here two years and never put grease down drain. Could this be from previous inhabitants? System has not been serviced since we've lived here, could that be problem? thank you

Answer
Sewage backing up into your yard or house does not have a direct relationship with "how long it would take for grease to clog system enough to back it up". In your situation, there are two most common causes of the back up. The first possibility is that your "out-going line/lines is/are clogged", and the second is that your "outlet baffle on the out-going side of your sewage tank is clogged" or "not functioning properly"

To determine what's responsible for the blockage, your "Distribution Box" (D-box) needs to be dug up. If the distribution box is dry, then know that the blockage is in the outlet baffle. And if the Distribution Box is flooded, then the out-going pipe/pipes connected from the Distribution Box and leading to the...