Do you know anyone who has a 4000psi Water pressure cleaner?...put the Zero degree tip on it and you probably could get more of it out than any other way...more than using chemicals which will leave a thick goo all over the sidewall that you will never get out, That goo will greatly increase the weight of the mast.

With the pressure cleaner you will eat right thru it and eventually blow it right out the other end...if it can strip the flesh right to the bone on a human it will annihilate the foam.

Regards,
Bob