118. Grease is very troublesome, because it is liquid and runs out of the sink readily while accompanied by hot water; but as soon as it encounters the cold surface of the waste or drain pipe, it solidifies and adheres to the pipe. The caliber of the pipe is thus reduced, and it will eventually be choked by the grease.

An ordinary variety of grease intercepter and trap combined is shown in Fig. 40. C is the waste pipe from the sink, B is the pipe leading to the drain, and A is a fresh-air inlet. The cover D should be large enough to readily permit the inside of the trap to be cleaned, and should be secured in position. The grease accumulates in a layer at G, and if allowed to become cold, will solidify into a cake, which can easily be removed.

This form of grease trap is mostly used for intercepting grease from kitchen sinks in large country buildings. As the trap must be large, in order to prevent the grease from entering the outlet B, it is usually .placed underground as near the sink as possible.

Fig. 40.

119. A chilling grease trap is shown in Fig. 41. B is the waste pipe from the sink, and D is the pipe leading to the drain. F is the vent pipe, and K is a local vent, or air-relief, pipe. The contents of the trap are chilled by means of a jacket A through which cold water is made to circulate.

Fig. 41.

Commonly, the cold-water supply to the kitchen boiler is used for this purpose, the water entering the trap through H and passing to the boiler through I. J is a close-fitting hinged cover. The grease chills into a cake at G and is removed by opening the cover.

The separation of the grease will be more perfect in this trap than in the one shown in Fig. 40, because the layer of grease is not disturbed by the water in entering or in leaving the trap. In Fig. 40 the entering water passes through the layer of grease and is liable to carry some of it along over into the waste pipe. A trap screw E is attached for access to the trap outlet. A petcock L is screwed into the water-jacket to drain it when required.