[PEMfish]

Study this;
I'll take you through it,,,
The water is in your tank
It flows over teeth into a overflow container.
There is the end of a U tube in there, it is sucking ( siphon ).
It flows through the U tube out of the tank.
The end of the U tube back there is lower than the one in the tank.
The water is now in a container out side the tank.
The container is divided in two by a wall called a baffle.
The water flows over the baffle
The top of the baffle lines up somewhere in the in-tank-overflow.
The water is now in section two of the container.
At the bottom is a bulk head with a pipe coming up out of it.
The pipe gets wider close to the bottom. The pipe is called a stand pipe.
Close to the top of the baffle there is a street T on the stand pipe.
Off the top of the T the pipe is caped.
In the cap is a small hole.
The water flows into the T and down Into the sump.
It gets filtered, goes over baffles, dose its thing...
Reaches the return pump
Up up and away.
The pipe leads into the DT ( display rank ). In the return pipe is two small holes above the water line.
The entering water makes the water rise.
It flows into the overflow.
Repeat.