Help with overflow

[mark]

Originally Posted by ed holland

is their an air trap. try puting a t in the line to let air out.
just my .02c

Already tried a 1" Tee, with the center pointing upwards (the Tee inverted how you would write 'T') both right at the bulkhead and also at the end of the horzontal run and no joy. On Skimmin suggestion, tried the Tee rotated 90° and placed on bulkhead (picture), still right on the edge of 300gph.