Hole size for external overflow

[AfaceInTheCrowd]

I’ve had a tank built which I asked for two holes to be drilled for
1 1/4” (32mm) connectors to use a external box like the synergy reef overflow these needed a 1.6” hole (42mm) ..I’m in UK so these aren’t available here but I have a 3D printer and can glue some glass together to DIY one
Anyway builder has drilled the holes too small at 36mm which is a bit less than 1 1/2” I think meaning that the connectors I’d have to use will reduce the size even further to just over 1” (27mm)
Will these cope with a 800gph (3000lph) flow from return pump? As I dont fancy drilling the holes larger If I can get away with it

Pipes inside external box are 1 1/4” (32mm)
Sorry for mixed measurements we don’t do inches here and I’m using Siri to convert

Hope makes sense thanks

 

[MoshJosh]

I am not familiar with the synergy, does this system use bulkhead? If the hole is only 36mm and if BRS's chart is correct, you are looking at using 3/4" bulkheads max. Looking at some old threads you are looking at 400gph at max flow/syphon each, so 2 will not be safe for 800gph pump IMO.

 

[Uncle99]

36mm is 1.4” is that not “bigger” than 1.25”
FlexPVC.com has a million configs from standard, metric and metric to standard.
My system was drilled metric but I live in Canada so I just had them ship me a metric to standard conversion.

 

[fishyjoes]

You could test it. Install the bulkheads and external plumbing (just ugly raw pipes without an overflow box) and run your return pump and see how the drains keep up. The bulkheads and piping shouldn't be very expensive.
If the drains keep up you can go ahead, if not you know you have to do something else.