It's not uncommon to make a simple mistake flushing your new jetski and finding out too late will literally cost you thousands.
This is the basics. Jetski 101. Seadoo and Yamaha are covered in this video.
Here's FIVE big reasons to have your jetski serviced in winter, which you might not have considered if you normally get your jetski serviced in Oct/Nov/Dec "so it's ready for summer".