How do you Flush the Upper Unit on Alpha 1 Gen 2

[pyrowetter]

I am replacing my lower unit on my 1999 Mercury 350 Alpha 1 Gen 2 engine. I stripped the gears on my lower unit and it was cheaper to replace with a new one. My old upper was alright according to boat shop. Now I think I need to flush the metal shavings from my upper unit before putting on the new lower unit. Unfortunately, I have been unsuccessful in finding out how to do that.

I am installing soon, so any help would be appreciated. Thanks.