Black stuff in gas tank

[ontherocks83]

So I just bought a 20' Checkmate speed boat (don't yell at me, it's just a toy to use when I can't make it to the sail boat) and I have been going through it mechanically and found a problem with the gas tank.

I pulled the fuel sender to take a look inside the tank as that is the biggest opening in the tank and I found the bottom of the tank peppered with black specs/crud. I stuck a stick in the tank and scraped at the crud and it can be dislodged with a little effort but it does not seem to be free floating.

Does anyone have suggestions on how to clean it or who to bring it to for such a process when there is no traditional access port? The tank is 47 gallons and only 7 1/2 inches deep but is very long and runs under the floor boards along the keel. Also the tank is glassed in and removing it is really not an option.