The most important thing - The Manual!

They always say RT*M - so here it is.  Your boat may be slightly different.  If you have a factory manual with changes, send it in along with your hull number.  Thank you!

Hull penetrations

It is important to know where water may be coming in.  This is the drawing I modified for my P-35.  I laminated it and put it on the head door so it is readily available to guests.  Right Click on image to enlarge.  Note that I changed the head to freshwater, and now the old head intake is used for A/C intake instead.

Your layout may be different.