A bell siphon is used in systems where the water needs to be drained. The siphon bell allows a tank of water to fill up to a certain point and then drain to any depth down to the bottom of the tank. The bell siphon system relies on gravity to drain the water.
Use 1-inch PVC pipe to act as the siphon and cut it to the maximum level you want the water to reach in the tank. When cutting the pipe, take into account the coupling that you will be using to attach the pipe to the bottom of the tank.
Use 2-inch PVC pipe for the bell; cut it 1 inch longer than the siphon pipe. Cap one end of the pipe.The pipe will create the siphon from the bottom of the tank.
Breaking the Siphon
Cut a ¼-inch flexible plastic tube to the length of the siphon pipe. Drill a ¼-inch hole through the cap. Insert the tube in the hole and glue it in place, making sure the glue does not close the tube. The tube's function is to break the siphon effect by letting air enter the top of the pipe when the water level goes down to a certain level.
Install a 1-inch PVC coupling on the bottom of the tank. Glue the 1-inch PVC pipe to the coupling. Alternatively, screw the pipe to the coupling if the pipe is threaded. Test the assembly for leaks in the system; water loss could eventually "un-submerge" and damage any pump in the tank.
Cut ¼-inch holes along the bottom of the bell pipe. Those holes will allow the water to enter the tube. The holes cannot be above the bottom end of the tube or the siphon effect will break too early. If you are using the siphon in a pebble or pea substrate, drill the holes smaller than the average size of the peas/pebbles so they do not plug the hole. Alternatively, you can use a filter to prevent the system from plugging itself.