Q: How often do I need to have the Grease Trap Cleaned out? A: Many local Authorities require that the system be cleaned out every 13 weeks or 3 months to start with. A Trade Waste Inspector will visit your premises from time to time to inspected the “Fatty Crust” or grease build up. He will then decide that your system needs to be cleaned out more or less often. It is not base on an opinion but on the measurements the Inspector records. Bigger systems always cost less in the long run, because your on going costs are less.