We have them a lot in Australia. Peggy's description is about right, although ours are a bit bigger - more like 18" wide x 24" deep x 30" long - maybe her's needed to be bigger to work. They retain a fair amount of water in them - a bit like a small septic tank - pipes enter and leave about two thirds or three quarters of the way up. However, the way they work is that the hot greasy water hits the cold water in the grease trap, cools down, the grease comes out of solution, coagulates, floats to the surface, and you get - guess what - grease trapped in the grease trap. If it's working properly, you definitely have to clean it out regularly, and it's not pleasant, because all the food scraps have settled to the bottom of the tank, which is acting like a small septic tank under its grease seal - anaerobic - STINKS!!! Better than grease-coating everything which should be breaking down in your septic system, though. Or keeping it separate but letting the grease make up its own mind about which parts of your drain its going to block up.(posted 9672 days ago)I worked in an office once which had been converted from an old hotel, and then done duty as a restaurant. They had a grease trap - legally required for food preparaton places feeding waste water to the sewer - which was half the size of a septic tank.