I just found out how to go down 2 water slides in one! heres how:
First stand here
Then hold down the right arrow key
and you will start to run towards the water slide.
One your on the water slide
DO NOT LET GO OF THE ARROW KEY
Then, you will circle around the small pool and start going down the other slide
This would be easier if i had a video but... my computer wont let me use screen-cast-o-matic. D: