Clogged thru hull/cannot close thru hull

[Sloopadagio]

Hi - yes, we have now joined that club....

We have a clogged black water thru hull. We are unable to close the thru hull so are unable to disconnect the hose as we are in the water.

We are wondering if it is possible to free the clog by hiring a scuba diver to use some sort of tool to at least clear the clog enough to close the thru hull? Or is the only way to haul out and do this in the trav lift?

And we have Marelon thru hulls so are concerned about damaging them depending on appropriate tool.

Thanks for all advice and help!