"how do you find out where its in?"
well it 'll be good first to know how it got in, and find the crack/hole..to fix it.
(or if it is through the screw )????
then there are different technics depending on how much water is in it.
You could drill little holes and set the board in a way that the water will drip out..
if you 've got a vacum pump you could suck the water out by the crack/hole
(after doing another little hole somwhere else in the board).
usually most of the water will get out slowly via little holes, sucking with the vacum pump just take the extra bit and tend to dry out the foam a bit more which is good. (using a vacum cleanner might work too).
in both case when sucking the water out you need another little bottle on the pipe so that the water doesn't go inside the pump/vacum cleaner.
I 've got a feeling that you live on the East coast?(from previous posts) no?,
if in WA you could always contact me and borrow the vacum pump to suck the water out.
good luck
