For horizontal drain pipes, a slope of ⅜-inch per foot length is ideal to keep the water flowing fast. Consider using 2-inch drain pipe for bathtubs instead of standard 1½-inch pipe.

• Sink drains: In the bathroom, sink drains suffer the way that tub and shower drains do, namely at the hands of hair and soap scum. Over in the kitchen, oil and grease from cooking are enemies ...

If your drain is clogged with hair, food, grease, toilet paper or soap scum, a drain cleaner can help. Plumbers recommend top options from Drano, Liquid-Plumr and more.