What is overflow area

Two pieces of glass plate and the upper and lower dislocation and the bottom of the tank is only adhesion, outside the glass plate (green glass plate) is higher than the cylinder bottom 1 cm distance, inside the glass plate (red glass plate) close to the bottom of the cylinder, two pieces of glass plate in the middle distance of 1.5 cm, two glass panels will be divided into two large range, the smaller piece of the area as an overflow area. The water in the fish tank is in the glass plate.

Overflow areas which can punch a hole can also play two holes, a hole is a water outlet, at the same time we need also the hose to the water inlet. If the play is two holes, one is water inlet, a water outlet inlet outlet is small, large.