It's not advisable to use Ditch Push-button, You will actually close both outflow valves, but aircraft's conditioning air, w/o exit, will pressurize the plane on ground and will be out of control afterward, since controoler will not control the valves anymore. Help me some one, but I believe that after using the Ditching p/b, reset may be performed only on ground, engines off.
Aside. I had some kind of similar experience w a MD83 (exhaust valve dimensions relationship to fuselaje diameter is bigger), but the person w the question was a Ramper and he, ISO stop a/c, asked a mechanic about....