My experience here is limited to one try only. I had the water pipe on the car and did not want to remove it. I sprayed some vaseline inside the sleeve, put the sleeve on the water pipe and then put the breather pipe in. I twisted my arm, I was late for lunch (which had severe consequences), but I put it in. I think important is that the ends of the pipes that go to throttle are more or less parallel and of equal length so that they fit in the hoses on the throttle. I see on the pictures that the water hose has clamps and the breather hose does not.
I am sure there is a better way.
I think that it is better that you have it out of the car. I just cannot imagine how you hold one pipe when you push the other. It seems to me that I would have a helper to hold the water line while I push the breather. The sleeve is quite strong, actually.
I cleaned the Mercedes bought sleeve from the protective coat with vaseline.
Do not forget the gasket at the throttle end that goes across the pipes. I have no idea why it is there, but it is seen when you look at the engine and it is supposed to be there, I guess.
