With this Installation Set the intake line of the external filter can be conveniently filled with aquarium water without detaching the hose connector. It fits 5/8 in. to 3/4 in. tubing. This closes the circuit and permits the water to flow to the filter automatically. At the same time, this enables easy aeration and convenient hose cleaning. This set is suitable for all aquarium heights and for all external filter makes with a shut-off device on the intake side. If this device is not available, a shut-off tap must be installed on the inlet hose.