If you put it on the hose before you start the engine, the water will fill up the engine.
Also, same thing if you cut the engine off before disconnecting the hose.
You need to start the engine, attach the hose with a moderate flow, not too much or the engine will not be able to flow it out, and it will back up. Run it for a couple to 5 minutes. then cut the water for about 5 seconds and cut the engine. In that order.
Otherwise, water backs up into the engine causing all kinds of problems.
Also, are you pinching hoses where the manual directs you to?