Access to Fresh Water Tank

[Chessie]

There is visible air in the fresh water feed to pump, resulting in pump not switching off. I have tightened all visible pump clamps and inspected pump and all appears fine. I assume that the problem is probably at the attachment to the tank. From the owners manual diagram it appears that the tank is located midships before the step down into the berth under the wooden floor veneer. How do you access this tanks without removing the flooring?
Regard
Alan