Similar query but specific to [2018] Sea-Doo Spark that I have yet to see a definitive answer for.
I know the score with clamping off the water inlet and, setting aside ideas of fitting a valve to the pipe itself, I agree with everyone who questions the physical reality of doing this given where the pipe is located in a Spark, how little access/leverage you have and the immediate proximity of a roasting hot engine/exhaust... and all while bobbing about in the water, and most likely, furious.
Having looked at the attached Cooling assembly drawing for the 2018 Spark (thank you riva racing) the pipe to be clamped during towing is identified as "1200" which connects directly, and exclusively, to the flushing adapter at the back where you connect the garden hose when flushing the exhaust out of the water.
My ask:
instead of trying to clamp the pipe in the engine bay, why can I not do what Ckrawiec suggested and block it at the flushing adapter using something like the bilge drain plug?
I don't see how the flow direction is relevant in this case as you are blocking the same, correct pipe (and on the same [inlet] side of its connection to the engine)... just approx 1m further along it.
Any air or water that's in there when you plug it has no outlet and hence while I can understand a little compression of any air, any pressure from another direction should equalise preventing further ingress.
Fully stand to be corrected
. Is there anything missing from the assembly drawing or other reason that would negate this?