Several forms of water closet are now made, designed especially for operation in places exposed to extreme cold, such as unheated stables, yards, etc. Water closets for this purpose cannot be of the ordinary style, that is, with the trap combined in the fixture, as the contents of the trap would be in danger of freezing. Therefore long hoppers are generally used on frost-proof water closets, the trap being generally of cast iron and located below the closet at sufficient depth to avoid danger of freezing. Various methods are employed in providing a flush. In some cases the flush is direct connected, while in other cases galvanized cylindrical flush tanks are used. The flush tank is sometimes placed in a pit below the water closet, and sometimes on the wall above it.

In the latter case the tank fills only when the seat is occupied. When the seat is released, a heavy weight attached to it opens the flush to the closet and empties the tank, any water standing in the piping draining through a small pipe into the trap.

When the tank is located below the floor it remains empty except when the seat is occupied. When the seat is pressed down, the tank fills with water to whatever extent the pressure will compress the air. When the seat is vacated the weight attached tips the seat up, closing the inlet to the tank, opening the flush to the closet, and the compressed air forces the flush through the fixture. When frost-proof water closets are located in cellars or basements of such buildings as factories, warehouses, and other buildings occupied, but not used as dwellings, they should be vented and local vented.