You sail on a different Chesapeake Bay than I do. After my first winter living aboard I bought an Electroscan. The only pump-out I could get in the winter was from an (expensive) truck that came to the dock, requiring of course that one be close enough to shore for the hoses to reach.
I have often sailed over an hour to get to one of the few marinas in my part of the bay, that have pump-outs, only to find that it is locked, or someone more important than me uses the fuel dock to transient tie, or it does not work.
My old marina regularly had at least one large boat blocking the pumpout (was also the gas dock), unless you could fit in a 20-22' finger. With my size boat, getting in and out is often a challenge as I would need to bend the boat around piles with lines - as there was no room to turn under power, or else back out from the way I pulled in.
In all cases they simply pump to a shoreside septic system that needs a lot of work....there is no "city sewer" in most of the NN....