I cleaned out the ski locker area last summer. I am embarrassed to say that I don’t remember the exact location of the tank in relation to the pump in the bilge.
When I cleaned it I put the plug in. Wet down the area and then scrubbed it with bilge cleaner. I let it sit in the bilge for a while, and then I took out the plug and hosed it down.
If I understand your post correctly, you sprayed water into the transom drain hole from outside.
I sprayed the water from the ski locker towards the pump and the drain hole. Try putting the pug in and fill the area with water if the battery is connected the pump should automatically come on and you will see water coming out of the starboard side discharge hole. Then you can take out the garboard drain plug and make sure the water flows freely out the back.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote."