leaking anchor box

[tjandoverguy]

i got some water in the boat ,in the forward birth, in some heavy weather
after looking at it, i removed chain ,plugged the drain and filled with water,sure enough it leaks, it is almost 3 ft deep
question how to waterproof

[Pelagic]

Trying to understand....

Are you saying the chain locker is leaking into the accommodations?

Your anchor locker is designed as a Wet Locker (that's why it has a drain)

From chain washing to heavy weather it should drain at lowest point .. and any water ingress is drained via a pipe to a discharge or overboard point.

Could the leak be at pipe joint at drain?

You didn't say what the locker floor and sides are made of?

If problem is not with drain plumbing then you have a container leak which could be cleaned and glassed to seal
Then lay some thin resined ply as sacrificial protection over the repair.