Water left in exhaust after starting on hose

[Yards76]

I picked a new sea doo from a dealer. When I was picking it up, the salesman started it (no hose connected). Once it started he shut it off, but a lot of water blew out the back end.
Reading the manual, the water should be turned off before the engine, so I would think most of the water would have been blown out when the service department ran it the first time. My concern comes from a comment the sales guy made, he indicated the guy setting up the skis has only been working there for a couple weeks.
Here is my question. How much water typically blows out the back when the engine is started after it has been ran on a hose?

The reason I am wondering, is if the set up guy stopped the engine with the hose still running, it could possibly force water into the engine.

I am probably overthinking this and I should trust that the dealer knows how to set up their skis. But since these are my first jet ski’s, I don’t want to assume anything.

 

[ski-d00]

The exhaust system always holds a lot of water, like a few gallons. It is very normal to have water come out the back when starting on the trailer regardless of whether it was run on the hose or in the lake. Usually a couple cups of water come out but can be more or less.

It is fine to start and run on the trailer for 10-15 seconds without water. If it runs too long or is revved up on the trailer, it will throw a high temp exhaust warning long beep which even that isn't a big deal as it will fix itself once it cools down.

You are overthinking but nothing wrong with being careful. As long as the engine starts and runs fine, they didn't do anything wrong.

 

[skiasylum]

A telltale sign that someone has flushed the engine with the water on and the engine not running and something bad has happened would be that water from the flush hose has entered your engine and mixed with the oil. The oil gets a milky appearance and can be seen on the dipstick.