The buttons on your toilet flush—why are there two buttons, a big one and a small one? Are you pressing the correct button, or just whichever feels right in the moment? Here’s the answer.

The seat disk predates the Korky flapper, so your toilet must ... single-button, dual-flush toilets,” Barnes says. “This gives us the ability to have a No. 1 and a No. 2 flush without needing ...