Ill try and post some this weekend.. there is air that gets into the overflow bulkhead so the flow is constant. You may get a gurggle thats the air flow being blocked by the water. There are ways to correct and air/water issues. Non tempered glass can be drilled with special glass bits. They sell them online and most glass dealers in the area will drill tanks.. call around for prices they very a lot in my area..
Bulkheads can be bought on line and the plastic screens that go with them can also.