t the circulation of hot water is maintained.
This will avoid the necessity of wasting water and waiting until the
water runs hot from the hot-water faucet whenever hot water is desired.

4th. The necessary fixtures, such as faucets, sinks, tubs, wash-basins,
kitchen boiler, water-back for the stove, water-closet, tank, and
fixtures. These may be now taken up in order and described more in
detail.

_Supply tank._

The attic tank may be of wood or iron, and its capacity should be equal
to the daily consumption of water. Its purpose, as already indicated, is
to equalize the varying rates of consumption from hour to hour and
between day and night. The minimum size of this tank would be such that
the flow during the night would just fill the tank with an amount of
water just sufficient for the day's needs. Of course, the additional
supply entering the tank during the day would reduce the size somewhat,
but the basis for computation given is not unreasonable.

Several accessories must be provided for such a tank. An overflow is
essential, and this is best accomplished by carrying a _pipe out through
a hole in the roof_. This must be ample in size, provided with a screen
at the inside end, and be examined frequently to make sure that the
overflow remains open. A light flap valve to keep out the cold in winter
is also a desirable feature for the overflow pipe. The tank must be
water-tight, and while it is possible to make a wooden tank water-tight,
it is wiser to line a wooden tank with lead or sheet iron. The latter
can be painted at intervals, so that it will not rust, and is safer than
wood alone to prevent leakage.

Care must be taken to give sufficient strength to the wooden tank; it
should never be made of less than two-inch stuff, and should not depend
upon nails or screws alone for holding the sides together. Figure 56
shows a suitable way to put together such a tank. Certain firms that
make windmills and agricultural implements generally can furnish
wrought-iron tanks, warranted to be water-tight, of suitable size to go
in an attic. Such a tank, as we have already said, should hold about
five hundred gallons and should therefore be a cube four feet on a side
or its equivalent. It needs to be very carefully placed in the house, or
else its weight will cause the attic floor to sag. A tank of the size
named will weigh a little more than two tons, and such a weight, unless
special precautions are taken, cannot be pla