Depends on the boat. My little 14 foot tinny the plug (one of those rubber expanding ones) goes in from the inside, any boat I've had bigger than that, the plug is usually brass or something similar and screws into an insert from the outside.
Since my permanently mounted gas tank covers the well inside, my plug goes outside. On my other boats, it goes outside just out of habit--but I use the screw type rubber plugs, not the flip type.
While changing the engine in my boat I cleaned the bilge and found the original plug in a thick dirt & grease concauction, it was ball chained to the transom and you would have to be a contortionist to get at it with the engine in. I removed it and use it from the outside. Stainless Steel.
My small sailboat has the plug inserted from the inside. If it ever pops out, at least I can find it while I'm sinking and limit the bailing.
Napa Scott
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Life's too short to drink cheap wine...
