Deck drain advice

[PassportJoy]

I have two deck drains on each side of my 43' sailboat. They are of adequate size and with the 1 1/2" drain hoses send the green water overboard rapidly. My problem is that at the aft end of the deck there is a puddle of water held in place by the cockpit coaming and the bulwark (area below the cap rail). I am considering drilling a hole and putting a small deck drain to any already existing through hull I can find. How can I "flush fit" or recess a through hull fitting in a very tight space? If I just drill a hole and install a mushroom head fitting it will stand proud and still allow residual water to puddle. Do I need to install a separate seacock or ball valve? Any advice would be welcome.

Jeff
Passport 43'

[Terra Nova]

There are flush fitting thru-hulls. No need for a seacock.