do you keep the boat in the water or on a trailer?.... either way, it needs to be different than what it is now. but on the trailer it will be an easy fix.
dont keep it for a pump out fitting, as a pump will lift the liquid to a thruhull fitting
above the waterline which is a much safer option.
if it was my boat, and I had no use for a hole in it, I would remove the fitting and fill the hole.
you can always drill another hole if you want one sometime in the future
on that boat, you can fill the hole relatively easy, as it doesnt take a lot of pounding and beating in huge seas.
and this is the way I would do it, as i have done in the past many times... others will have other techniques that may work equally well, or better, depending on how much work you want to put into it....
after removing the fitting, sand the hole to insure its clean, and there is no forgotten debris that may prevent adhesion of the epoxy.
then on the inside of the hull, taper the edges out about 3x the thickness of the hull at that point. only dig into the hull thickness about half way or slightly more, or you will have more filling to do.....
then cut a piece of mylar, or milk jug plastic, or cottage cheese lid (or some similar type of stiff plastic) slightly larger than the hole on the outside.
tape it over the outside of the hole firmly....
mix up some marine tex (or some other epoxy
paste) and fill the hole from the inside, fairing it out but not pushing too hard so as not to push the plastic "form" away from the hull.... you can lay a piece of saran wrap over the epoxy and smooth it out now, or do it later with a powertool after it hardens.
depending on how well you filled the hole, this would normally be enough for a lot of people, but not for everyone, so....
after it has hardened, taper the hole from the outside, but only a little, and use either the white marine tex or gelcoat to fill the depression.... tape a larger piece mylar over it to smooth it out even with the surrounding surface and let it harden..... then use a nib file if necessary to fair it down even with the hull, or fill with more gelcoat or epoxy as needed.
TIP... when filling a hole this way with marine tex, I make sure the epoxy is at or above room temp so it flows nice, then I mix up enough so that i can place a dollop of it into a plastic sandwich baggie... into the corner. then i will squeeze it down and twist the baggie so its all contained in the corner. and when im ready to apply it, i nip the corner of the baggie and squeeze the epoxy in to the bottom of the hole... this insures you displace the air as much as possible and dont leave any hollow spots.
there may be only minor filling and fairing to do on the outside if the hole was filled completely to the form plastic.
when the epoxy is warm, it begins to stiffen up fairly quickly as it cools, so work quickly once you get it mixed.
