Figure 2-4. Soakage trench with barrel filter grease trap.
b. Grease Traps.
(1) Baffle grease traps. A baffle grease trap may be made from a drum (see
figure 2-5 A) or from a watertight box (see figure 2-5 B). The drum or box is divided
vertically into an entrance chamber and an exit chamber by attaching a wooden baffle.
The baffle should be placed so that the entrance chamber will be approximately twice
the size of the exit chamber. The baffle should hang to a point within 1 inch of the
bottom. A strainer, which may be made from a small, perforated box filled with straw,
hay, or burlap, is placed in the entrance chamber. An outlet pipe is inserted into the exit
chamber about 3 to 6 inches below the top as an outlet to the soakage pit. This baffle
grease trap is usually placed on the ground at the side of the soakage pit with the outlet
pipe extending 1 foot beneath the surface at the center of the pit. If a grease trap is not
watertight, it must be placed partially under the ground.
(a) Before the grease trap is used, the chambers are filled with cool
water. The waste liquid is poured through the strainer, which retains any solids. As the
warm liquid strikes the cool water, the grease rises to the surface of the entrance
chamber and the liquid runs under the baffle, filling the exit chamber. When the liquid
reaches the outlet pipe near the top of the exit chamber, it runs through this pipe into
the soakage pit. Unless the grease trap is of sufficient capacity, the warm greasy liquid
poured into the trap will heat the cool water in the trap, thus allowing the grease to
remain uncongealed and to pass through the trap. The efficiency of this grease trap
can be increased by constructing it with multiple baffles. Also, a series of traps may be