Grease traps (fig. 11) are not recommended for the average farm, because they clog easily and require frequent cleaning, but they are desirable for boarding houses and tourist camps where large quantities of grease are produced. The septic tank if of proper design and size will take care of the normal grease from most farm kitchens.

The traps must be several times larger than the quantity of greasy water discharged into them at any one time, in order to allow the greases to rise, but they should not be of less than 30 gallons' capacity.

The trap is best located in an accessible place in the basement or under the house close to the source of grease and safe from frost. Outdoor locations at shallow depths require a covering for insulation against freezing. Grease traps should be connected to the kitchen sink only and not to laundry, shower, or water-closet wastes. They must be cleaned periodically for satisfactory operation, and the outlet should be properly trapped.