Intake is 3/4" fittings so a 1" hole. For the tank the Internal style usually drains through a 1 1/8" fitting (1 3/8" hole). The External however has been draining through a 1 1/2" fitting. Its all going to depend on what exactly you need. The External KayaTanks are designed specifically for certain boats.
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Cj@oeexpress.com