Refrigerators should never, under any condition, be directly connected to any part of the drainage system.
This restriction makes it necessary to provide connections for the refrigerator on an entirely different principle from those of the regular plumbing fixtures. The refrigerator should drip into a pan beneath it, which should be trapped, the waste from the trap dripping into an open sink.
The sink should be trapped and vented in the usual manner, and may be connected to any soil or waste pipe.
Plate VIII. Refrigerators - Safe Wastes - Tank Overflow - Special Wastes
The use of the drum trap is good practice, as it may easily be cleaned of the slime and sawdust which collects in considerable quantity. It also has a much deeper seal to withstand evaporation when the refrigerator is out of use.
The methods shown in Figs. A and B amply protect the refrigerator, for there is not only the trap usually found inside the refrigerator, and the other two traps, but also the two breaks in the connections.
The outlet from the refrigerator trap should discharge as far from the sink outlet as possible. It is preferable to drip into a sink in common use, as the renewal of its trap seal is ensured, but if impracticable, a special sink may be employed.
It is permissible also to discharge the refrigerator waste into a cellar-floor drain, yard drain, or into a trap provided with a receiving funnel. In the latter case it is necessary to provide a brass screw cover or a gate valve for closing the trap when the refrigerator is not in use.
The waste from the refrigerator should never be less than 1 1/4 in. in size. Short wastes and traps may be of lead, but long lines should be of galvanized wrought iron.
The refrigerator waste should have as sharp a grade as possible.
Fig. C represents a desirable form of refrigerator drip pan. The box is lined with metal, formed so that all drippings entering the pan flow toward the outlet, which is provided with a strainer and brass screw cover, the latter for use when the refrigerator is not being used.
The requirements for refrigerators apply also to ice boxes, or any other receptacle for food or provisions which it is necessary to drain.