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Dream 'Inn III -- 2008 400 Express
2002 FV 342 on Lake St. Clair - Past Commodore SHC - Vessel Examiner USCGAUX
If they can pump it out at a marina there should be a way to do it at home.
I have used a shop vac years ago it will collapse your holding tank and possibly crack it. To much CFM for the small vent tube. A dieafram(spell check) type pump maybe better. Or maybe let some air in as you vac it will clean out the tank. Maybe some rubber gloves and a face shield from experience.
...keyed switch on the macerator with the key not being stored in the switch...