Oh boy ... I'd fix it from the INSIDE as you don't know where it is migrating to in order to dump out that keel weep hole.
But I would not just dump water in, in one spot, like filling the hull was done. You might have to remove the floor and try putting water on a keel area only 2' long or such to help identify the area that is weeping. You could even apply clay in areas to make dams to help isolate the damaged area down to a few feet fore and aft. With a floor in your way ... uggghhhh.
Option - Now the epoxies typically used (West System G-Flex 650 or Glu-Vit) do weep and migtrate, so if you turned the hull completely over you could try to get it in to seal the area from the weep hole access. Here's what you'd have to do. Let's pretend the keel weep hole is 2' from the bow portion (of the keel itself, not the hull). Have the hull tipped to one side
just a little bit and with the bow down
just a little bit, so if you put the epoxy in, it will flow forward and off to that one side. Let's assume that is the right side as looking at the hull upside-down and towards the bow (yes, this is actually the 'port-side of the hull, but stay with me, as you're working on the running bottom).
Now keep in mind if there is a leak ... then epoxy WILL drip out into the boat, but you say there is a floor installed, so you may get any resulting epoxy damage to the inside ... but you will also not know how much is getting into the boat. But suffice to say, if you put in 1/2 a gallon, there is the likelihood that 1/2-gallon could go into the boat! So don't use 1/2 a gallon, which was just a gross example used to make a point! Try a capful and put it into the weep hole to help seal the 'forward right part' of the hull. When dry or cured, tip it to the left and bow down
just a little bit and try sealing that "side & forward" area. Cure.
Try again, this time with hull tipped to the right side side
just a little bit with the stern down
just a little bit so the epoxy dripped in or injected in with a syringe tends to migrate to the right side and away from the forward section you had previously treated. Cure. Repeat to the left side. You might even see epoxy weep out from the keel onto the bottom of the hull, but be aware that that doesn't mean that is a leak that penetrates the hull.
Cure. Then maybe even
repeat the steps above. Cure agin. Then try tipping the hull over again and filling it with water, to see if the epoxy may have made a seal???
Product - I personally would NOT use a very thin, vicious epoxy for this like the 2 mentioned above, but one a little closer to being closer to a syrup than that of water. You do want it to flow and migrate - yes - but not be soooooo thin that it just drips through the holes and doesn't fill them. I'd consider buying the epoxy sample kit or the small epoxy/hardener only kit from Raka Epoxy and would likely use a fast cure hardener, so it sets up ... which if that is at or around a hole, should seal it.
www.raka.com .
You might even do a 'test' of your epoxy mix against the outboard edge og the keel-to-the-hull to ensure it flows down that edge ... that could give you confidence it will flow when injected inside the keel - where you can't see! And just to throw it out there, I am not sure if Flex-Seal makes a liquid product, but whereas that is likely thicker ... if it flowed good enough for you, that too might seal without making a mess 'inside' the boat.
FWIW I did have to totally remove the entire 10+ long center keel on my saltwater tin to fix it properly, link =
Center keel removal & repair – On a SALTwater tin And yes ... it was UGLY under there!
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