On the surface, the logic seems sound. Drano clears clogged pipes. A dishwasher drain is a pipe. Ergo, Drano fixes the dishwasher. But this is a mathematical fallacy that could cost you hundreds of dollars, a trip to the emergency room, or a new kitchen floor.
Panic sets in. You don’t have a plunger handy, and the hardware store is closed. Your eyes scan under the kitchen sink and land on the familiar orange bottle: drano for dishwasher drain clogged
It happens around 8:45 PM. You’ve just finished a lasagna that was heavy on the cheese. You load the dishwasher, hit “Start,” and walk away. Twenty minutes later, you return to a half-inch of greasy, gray water sitting in the bottom of the tub. It isn’t draining. On the surface, the logic seems sound
Sometimes, people use Drano, run a rinse cycle, and the water drains. They think they’ve won. What actually happened is the heat from the reaction temporarily softened a grease plug, allowing it to move further down the pipe. Now, instead of a clog at the filter, you have a clog three feet downstream in a narrow ¾-inch hose. That new clog is mixed with melted rubber and lye crystals that have re-solidified into a concrete-like mass. At that point, you aren't unclogging it—you are buying a new dishwasher. Ergo, Drano fixes the dishwasher
Most Drano products foam. Dishwashers are sealed environments with spray jets. If the chemical foam rises even an inch, it gets sucked into the spray arms and blown all over your dishes. Even if you rinse the machine ten times, residual caustic film can remain on glasses and baby bottles. That film causes chemical burns to the mouth and esophagus. No amount of clean lasagna is worth that risk.
The dishwasher drain hose loops up high under the counter (called a "high loop") before descending into the garbage disposal or sink drain. When you pour chemicals into the dishwasher basin, they don't just flow straight down. They slosh. As the pump tries to engage, it often pushes those undiluted chemicals back up the high loop and out through the air gap (that little chrome cap on your sink). If you have a countertop air gap, a geyser of boiling lye can shoot directly onto your counter, your faucet, or your hands.