LIS is not a "no discharge," zone (although just about every harbor on it is, and now any part of it that CT claims as their waters)...but that does NOT mean that it's legal
to dump a tank in LIS. It's not...which, while it does not make it illegal to have a macerator installed on your boat in LIS, does make it illegal to use it in LIS.
You must be outside the "3 mile limit" to dump a tank or flush a toilet
. That does not mean just three mile from the nearest shore in a bay, sound, lake or river...it means that you must be in open ocean at least 3 miles from the nearest point on the whole US coastline--iow, in international waters--to dump a tank legally anywhere in the US.
However, except in the 90+% of harbors on LIS that have been designated "no discharge," the discharge of treated waste from a CG certified Type I or II MSD (treatment device) IS legal
on LIS...and the whole Chesapeake Bay
except for Herring Bay...and at least 90% of the rest of the waters between LIS and the FL Keys.
So unless your bushy bearded guy at the pumpout dock
was referring to CT waters, he doesn't know what he's talking about. But then, there's a LOT of that going around!
Btw...pumpout and thoroughly rinse out your tank...and then put either a y-valve or a shutoff valve in your tank discharge line so you can cut off the flow from the tank to the macerator if you have to...which you will...'cuz all macerators eventually need new impellers, or even outright replacement.