Chris Plastow
You are getting into a very technical operation. There are two ways to do this, drain the water on the outside for long enough to seal the inside or inject the inside with polyurethane foam. In both cases this is a job that must be done with precision and understanding! If you are in the London area, I could help you, if not, call Koster Aquatic on Monday, they will be able to help you with advice. Avoid cowboys at all costs.
