Notice how this kind of thing happens all the time with little kids. They see a problem and jump in to solve it, no matter the cost. In my view, it's a sign of their curiosity and want to help, even if it backfires. You get a plumbing lesson now, but he'll remember helping for years, your mileage may vary. It's one of those parenting moments that's equal parts frustration and pride, from my experience.