In the UK lemonade is a carbonated soda. I thought that was the root of the joke, with a cultural confusion. The other commenters seem to think it’s a pee joke? But if it was, it wasn’t funny so I think I’m right.
That said, my interpretation isn’t funny either? What is this post?
Think it’s referring to this kinda squirt.
to anyone who doesnt believe this reply, look for a ‘view source’ option on the comment, or if on mobile consider using URLCheck