AFAIK, the important factor is that any overboard
discharges can be securely closed off and sealed. Exactly how that is accomplished is up to the builder/installer.
So any of the "treat, then discharge" type 1 or 2 MSDs are not OK.
Composting is OK.
Any reasonably well-built and well-installed holding tank
should be OK as long as the discharge and/or Y valves can be locked or sealed in the closed position somehow. If the head
has a direct overboard
discharge, consider disconnecting it from its seacock and plugging it while on the Great Lakes
. (Nicholson58's locking bar and numbered seal should satisfy any reasonable inspector.)
Stay in the officers' good books
if they do ask to come aboard, and you should be fine. But also note your pump-outs and installation/removal of the discharge valve lock in the ship's log, so that in case you do get an invalid ticket/fine, you can quickly prove to a judge that it should be tossed.