----- DRILL TANK----
If you want the water level to be higher, all you have to do is add an extention to allow the water level to rise.
----- NON DRILL TANK----
here is how the overflow works
Here is a DIY version. Its much cheaper and works the same way.
----- How to build a Neoprodigy DIY overflow----
Im using a 1-1/4 pvc pipe :
PVC primer and cement :
Primer the ends :
When its all cemented :