Duck bill installation

[Flatiron]

I want to put a Duck bill Drain in the right rear corner of the cockpit in my Hydro. What size should the inside dimension of the drain be ?

[laddies]

The duckbills that we used fit into a 1" drain tube.
Heres a link with info. https://www.iboats.com/shop/moeller-...o-flapper.html