Elephants love to play with water, especially when someone is near.
When the tail is lifted, the animal drinks water. It is best to keep the entire elephant under water while filling it. Push the tail down while aiming the trunk and make someone really wet. Two elephants make real summer fun together.
Too small? Just scale it up. To be printed legs down. This thing is not for beginners. The inner surface of the elephant should be very smooth. Polish it and use plenty of grease to reduce friction and make it water tight. Two O-rings complete the piston. The dimensions (diameter/thickness) of the O-rings are critical (see photograph).
Open SCAD files of the four components are attached. Especially the piston might need some trimming, depending on the surface roughness and the O-rings.

The kids will love it!