24
MAINTAINING FISHES
However, the above system has some definite advantages. It can be used for tanks containing sand, it
primes rapidly and its suction force can be easily adjusted.
VALVE TO ADJUST
SUCTION
WATER LEVEL
INOICATOR--f VACUUM V
V CLEANER j ^
50-GALL0N
STEEL DRUM
(^
RUBBER
GARDEN
HOSE
3/4" I.D.
%=J
AQUARIUM
GATE VALVE
4. A suction drain that may be used for both cleaning
and draining tanks not equipped with gravity
drain.
Running-water tanks and large, still-water tanks
should be equipped with a gravity drain system. The
drain may be plugged by a riser pipe which serves as
an overflow. It is usually convenient to combine the
overflow and drain. If incoming water is colder than
the tank water, it will sink to the bottom and an exchange of water will be insured. More often, however, the incoming water is the same temperature as
the tank water. In this case exchange is made possible
by placing a larger pipe over the overflow pipe thus
forcing the water that overflows to rise from the bottom of the tank (Figure 5).