Change thru hull on front fish box on 23'

[Billpotter]

If you remove the old drain sleeve, and the material between the hull and the fish box liner is solid when you poke around with a screw driver, you can use a brass sleeve bathed in 5200, and your flaring tool. If the area between the panels is in poor (mushy/ loose) condition, I'd use a suitably sized bronze thru hull (same hole size or larger) bathed in 5200. That should, with regular monitoring for leaks, provide a solid reliable seal. It worked on my 18 for 12 years.

Good Luck!