Grease trap installation must be carried out by a licensed plumber. Your plumber will be able to advise you on the best hydraulic design, venting and backflow prevention. Your local water authority will require your plumber to supply a Certificate of Compliance for their work.
Grease trap installation can occur either above or below ground depending upon the circumstances of your location.
If the grease trap is located above the waste water collection point, a pump tank will be required to pump the waste water up to the grease trap.
Ideally, the preferred grease trap installation is where waste water can drain by gravity to the grease trap and then by gravity out to sewer. This avoids any maintenance issues associated with a pump unit.