Contact those marinas for pump out :
In Great Salt Pond:
Champlin's Marina: Ch 68 or 401-466-7777
BI Boat Basin: Ch 9 or 401-466-2631
Payne's New Harbor Dock: No VHF call 401-466-5572
On the East shore:
Old Harbor Dock: Ch 12 or 401-466-3235
Ballard's Inn: Ch16 or 401-466-2231
Let me know if you'd need more information about the mooring and anchorage areas and nav aids... I don't live there, but I've been there with my sailboat, which has a porta potty, and powerboat, which has a full head system. If you can use the shore services, you'd not need the use the porta potty. However, for over nights on mooring or anchor, just contact them and let them know that you are coming. They are really helpful. But I wouldn't trust the shore hands on East shore, since they were not so experienced last summer.
I'd recommend you to call the places in advance to ask any specific questions you may have.
I hope that helps.
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