I'm not proposing the Orion but it may be a remote possibility. As I understand the museum aircraft they are still only on loan from the RAAF. Loans can be recalled?
My point is that an FAA certified dump system exists and is in use for both Orions and L188s.
Looking at the current L188 operators, they are moving to the Bae 146 aircraft and that seems to be the way to go,given hull availability and local experienced operators.
Wunwing