What's this bolt for?

[jr438234606]

Now that I have a clean, painted bilge, I've noticed a small amount of seepage. There is what appears to be a large "nut" on the interior, just barely visible in the lowest part of the sump.. I located a picture of the exterior of the keel and deduce that the picture below shows where it is. I assume the seepage is coming from this bolt, or drain plug, or whatever it is, but I can't sure. But I sure am curious as to what this is.

[Maine Sail]

Most likely a drain plug for when you're on the hard to keep the bilge dry..

[Rockter]

Not that deep it isn't.
No bilge ever goes down that far.
Send us a close-up picture of it.