1- With the hole cut in the tape press the thru-hull tightly into the hull and lightly trace it with the X-Acto knife then peel away the tape.


2- Once the ring of tape has been pulled off sand away the bottom paint that would be under the thru-hull. Sand until you get to gelcoat or a barrier coat as shown here. This will create the best watertight seal between the hull & thru-hull fitting.