Maximum drain flow through a 1 1/2"

[justincgdick]

Are you running the drain at full syphon (with a gate valve)? A 1" drain at full syphon adapted to 1 1/4" pvc should handle upwards of 2000gph.

I can't see the 1.5" having any trouble if you go full syphon.

[daplatapus]

This is one calculator I've used in the past and it seems to be really close:
http://beananimal.com/articles/hydra...-aquarist.aspx

According to it a 1 1/2" full siphon (with a submerged discharge) at 4' of head can take over 5000 gph.

[madkeenreefer]

Should be fine at full syphon, but it may be alot of flow through your sump which may reduce the effectiveness of your water treatment depending of your sump design of course.