water in hull

by stew
(country)

Hi i purchased a 4.9m markham whaler(sharh cat) with under floor fuel tanks. On inspection of tanks i noticed water in the hull i lifted the front of the boat up and undone the bungs and left to drain for a week but nothing come out i pushed a bit of dowl up the hole and it felt like it was pushing through the boyance is it posable the boyance has colapsed and blocked up the holes as you can not get to look under the floor.( thanks for your help )