Yes you could do that. I’d still suggest peroxide. But my Peroxide Fix hardware sticks up quite a bit — pretty close to 14 inches, maybe. In the end, peroxide or draining, you get the same thing: oxygen is introduced into the tank that kills anaerobic bacteria. The peroxide is about oxygen. It’s not about “bleach.” Draining is just more time-consuming. We’re not overly fond of tankless heaters, but this might be a place where one would make sense.