In WSSC's territory (Washington Suburban Sanitary Commission, PG & Montgomery counties, MD) we have to reduce each tailpiece on each compartment to 1/2" & provide an airgap where it dumps into the main trunk line. This in theory slows the water going through the grease trap along with the flow restrictor. The main trunk line can be 2" or 3" depending on the size of the compartments & how the inspectors feeling that day
. Typically, we'll pipe everything into a floor sink if one is available but it can be piped directly into a drain at the wall & they will not allow a commercial disposal at all. They're also strict about grease abatement so a trap or outdoor interceptor is a must.
They've been giving out FOG violations left & right to everybody, restaurants, churches, etc. I think it's kind of messed up that they treat a church that cooks 2 meals a year the same as KFC
DC on the other hand, you don't need to reduce the tailpieces & can tie directly to each compartment. You can have a commercial disposal as long as it doesn't go through grease abatement equipment. DC's like the wild west in comparison to WSSC