Bulkhead Flow rates

While many factors can impact the flow rates of bulkheads, these rating will serve as a rough idea as to what you can expect out of a bulkhead.
gph = gallons per hour

For bulkheads not relying on gravity(Drilled back or side wall..or PVC overflow) AKA a horizontal overflow. 

1/2" =  100gph

3/4" = 200gph

1.0" =  350gph

1.25"= 580gph

1.5" = 840gph

2.0" =  1500gph

For bulkheads that rely on gravity(Drilled threw bottom of tank) AKA a vertical overflow.

1/2" = 150gph

3/4" = 340gph

1.0" = 600gph

1.25" = 940gph

1.5" = 1350gph

2.0" = 2400gph