The most effective way to resolve clog issues is to thoroughly jet/clean that pit initially and see if your problems continue.
Since that device is installed on your system, it is a good thing since detergents and grease can disturb/interrupt the digestive process of your septic system.
Either have a septic cleaning service pump the pit or if it is small enough, you may be able to use a shop vac and clean it yourself. Expect the most horrible looking stuff and smells in doing so, it ain't pretty to say the least.
I used to have to clean numerous grease pits/tanks as a union service plumber and I would try to avoid them at all costs. Part of the job though and we had a dedicated shop vac for the job.
In your situation, if the pit has never been cleaned, it most likely has a hard-caked top to the surface that is restricting the inlet leading to the outlet. That happens quite often and once removed/clean the system operates without error.