posted 09-15-2013 10:32 AM ET (US)
Erik,Given the lack of responses specific to the Outrage 250 perhaps your question could be best answered by your local Boston Whaler dealer.
Generally, if there is space for a porta-potty a vaci-flush will fit. The real question is where to put the ancillaries and plumbing although the pump out fitting would probably serve for either waste handling system if properly connected.
If you want the capability to use the system offshore with a "Y" valve to bypass the holding tank that will complicate the installation and require some extra space. If you want the capability that should be made clear to whomever you consult on your question.
Butch