For flushing, you can use the "blue port" (but get that cap back on TIGHT when you're done!), or you can get a set of "muffs." Every boater should have a set of muffs in any case. Spend a couple bucks extra and get a pair that feeds both sides of the drive, not just one, like these:

They're available from many places.
Be aware that the Volvo factory manuals 1) contain very few part numbers, and 2) are very much written for the mechanic with a "just replace it" (as opposed to repair when possible) view. That isn't to say they're worthless - I have a set and am glad - but a Seloc manual is a good addition to have. Also, Volvo does publish a "parts catalog" (which is really just a list of part numbers) that I think you can download from their site. I'll look for it when I get a minute.