You don't want a "vent" thru-hull...those are designed to keep to sea water out of the fuel and water supply, so don't allow the air exchange necessary to create the aerobic environment the tank, essential to preventing odor out the vent.
What you DO want is an open bulkhead or "mushroom" fitting. You have my book...there's a photo of one on page 41. That one is marelon...PVC ok, nylon is not because it's not UV resistant and will turn the fitting into dust.Also available in stainless steel or bronze. Another major advantage to the open bulkhead fitting is: you can prevent vent blockages by putting a hose nozzle against it to back flush the vent line every time you pump out and/or wash the boat. Anything that's set up housekeeping in it will just get a water slide ride into the tank. Unless it's a mud dauber nest (common in the spring). Those have to be broken up and scraped out with a screwdriver blade or an ice pick.
As for a new vent fitting on the tank, the Uniseal is what you need
UNISEAL I suggest you call them to order it because you need the size that fits the OUTER diameter of a 1" hose (nominal hose sizes always use their INNER diameter and hose wall thickness can vary considerably).
--Peggie
