So you got the ball on the playground floor. But how to get that pesky ball up the slide? If you just keep blasting in with water, it will just bounce right off the stego's face and you're gonna have to chase it around the place.

Well, here's where your trusty step stool comes in. Simply place it in front of the slide as pictured:

And then also as per picture get the ball in the corner between the slide and the stool.

By crouching and facing the slide you can then get a nice angle on the ball and actually get it up the slide. I recommend the red nozzle and no extensions as it gives the ball most oomph. Once over the lip of the slide it super easy to just get it rolling all the way to the top.