Clog drain tube

[nymack66]

I have a clog in the drain tube which runs below my fuel tank, I am not sure what it is since the electrical snake (stiff manual wire) refuses to clear it.
During and after my hull rebuild it was clear, I went Boating and during my wash down observed the water build up.
I am now convince I will tear out the hatch liner below the deck to expose the tube in such a way I can insert a small copper tube to clear the line.
Has anyone ran into an issue like this ?
Below is a photo with the old tank removed and cleaned.