He's a fan
Too bad I only had red food color for the water play wall.
I grabbed some bottles from the recycling, and a funnel and tube from the workshop and screwed them to the fence -- not tight though -- so he can tilt and twist and rearrange things, discover his own method. I also left a couple different caps on the bottles, to open and close.
I did have to buy the tub however. But there are a million and one uses for a galvanized tub.
Next on the to-build list: a shaded sand box play table!