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Am I missing something here. If I'm counting the numbers indicated on the right to the left of these replies there were 7 or #8 whenI started this repky which would show #9. None of them answered the question as no real info was given by the OP
If the OP has a certain type 17' Whaler i.e. a Montauk 170 with a Merc. 90 on it in a slip with fresh H2O available it seems to me pretty easy. You hook you H2O hose up to the back center of your engine.
Mercury's procedure varies by engine size and series. Smaller and midsize four-stroke outboards use the flush port at the rear of the engine. The engine must be warmed up to open the thermostat and circulate water throughout the engine's cooling passages completely. The engine can be vertical or tilted. Remove the prop, and run in neutral at no more than an idle speed for at least five minutes. The water supply should not be opened more than halfway to regulate water pressure.
If you are saying you can't reach that you can always have an extension on it.
Yes it doesn't flush the pump out as good but it gets thru all the cooling passages.