I played through 20 levels to get a proper impression of the game.
To be honest, apart from level 17, most of the puzzles felt quite easy. I found that I could usually solve them by simply clicking on each pipe until everything fell into place, without really having to think about the solution.
I'm not sure what difficulty level you're aiming for, and perhaps the later levels become more challenging, but personally, I would have liked the puzzles to require a bit more thought. Level 17 stood out to me in that regard.
One small visual issue I noticed right away: the "START" and "GOAL" labels are aligned on the same line, but while "START" looks fine, "GOAL" overlaps with the toilet image. It looks like a small UI issue.
Overall, it's a nice little game! The difficulty wasn't quite what I was looking for, but I can see how the simple, relaxing gameplay could appeal to other players. :)