maybe use 32mm bulkhead fitting from hansens products nz
think it requires a 40mm hole but get a fitting and check before drilling
pipe work from tank as large as possible to save having to redrill later if you need more flow through sump
they bred in a brackish tank with monos and puffers
ie: they mated, carried young then they went free swimming
never raised young though to adulthood and then breed again
that is why i posted the pic of the net
you can still breed from him just need to let future buyers know you are unsure of the parentage on the male
maybe call them thick skinned sethg
nice fish that would pass on nice genes if you are selective in the breeding
it will work, just a syphon overflow is not the most reliable around as it can be subject to air bubbles forming in it and restricting flow
done the same in the past but ended up drilling tanks and plumbing together