This, right here, is the million dollar question. There's ZERO reason to add holes to a boat that allows water in, if you don't have a reason, and empirical evidence that you're not doing more harm than good. With the issues this one single solitary stupid idiotic fitting introduces (is my bias showing?), this should have been eliminated long ago, or actually addressed. The issue ISN'T that it's a plastic fitting, it's that an absolute shit fitting was used, with no attention to the fact that it often was improperly sized or cut short. Adding a metal sleeve doesn't fix the fact that it's not sealed, doesn't reach the interior, and it's an easy step to miss or ignore, sealing it up, in the manufacturing process.
Add to that, the production line seems to have days where the hole is drilled with precision, and other days someone is shooting off a 45 and happens to hit the spot where they think a drain might be useful, and that one stupid hole in the boat becomes a larger liability, and leaves a mess for an owner to address on their brand new boat.
This isn't IKEA furniture that's cheap and comes with certain expectations of quality and the need for immediate effort and attention by the owner, this is a severl-tens-of-thousands-of-dollars item, and it's not unreasonable to expect to not have to immediately fix/repair/replace a $5 fitting for such a stupid reason.
The REASON to use a metal fitting (and therefore a more expensive part,
@Yamaha), is that, since you're having to fix this screw up, spend a minimal amount of money to UPGRADE this, rather than use plastic and have it deteriorate - as ALL plastic does in the sun - and have to replace this later on down the road, for yet another reminder that this is/was a problem that shouldn't have existed in the first place.
This forum should NOT be your R&D, but if you're going to use it as such, FFS pay attention and stop trying to save pennies and use a PROPER fitting that can be sealed off, plastic or otherwise.