I think this is a very frustrating thing to maintain.
Do a search of this. It involves a turkey baster, a mirror, and maybe removing the exhaust.
I personally believe that this truly never gets changed except on a bottom end rebuild.
Let the other people chime in.
I have a DI and it's impossible. I also think mine gets oiled through the oil system. But the damn Seadoo manual isn't that great cuz it's done for the non DI model with a few excerpts for the DI.
Look at my name and search my posts to see our ideas about this.
Nate