Chemical drain cleaners are among the most dangerous household products--hardly a shocker, since these lye-based formulas are meant to dissolve plugs of grease, soap, hair, and ground-up food. Yet most don’t clear undersink clogs as well as old-fashioned mechanical methods, including the humble plunger.

Another surprise: Chemical products labeled “heavy duty” or “professional strength” often proved less effective than their regular-strength counterparts in clearing kitchen clogs made of grease and food, and bathroom clogs of soap, toothpaste, and hair. And two foaming chemicals, from Drano and Liquid-Plumr, tanked altogether in our tests.

Crystals, another type of chemical drain cleaner, attacked clogs with a fury. But if the crystals are exposed to aluminum, a common material in some older sink trim, they can generate a choking cloud of lye-laden gas. Plus, mixing these products with different chemical drain cleaners or with common household cleaners, especially those that contain ammonia, can cause the mixture to burst out of the drain. (See Safety). And if you accidentally pour too much of one product, Roebic Heavy Duty Crystal Drain Cleaner, down the drain, it can turn into a solid, stonelike block that’s almost impossible to remove. Given these potential dangers, we don’t recommend using them.

Biological cleaners, such as Citra-Drain and Zep, use enzymes or bacteria to chew through clogs. Besides posing less of a health risk to humans, biologicals are less likely to harm septic systems because they don’t kill beneficial bacteria. But they’re wimpy when it comes to quickly removing clogs. However, they should be useful at keeping drains free of organic material once clogs have been cleared.

Mechanical drain cleaners are almost universally safe, effective, fast-acting, inexpensive, and environmentally friendly. Our advice is to invest $75 or so assembling a clog-clearing kit with one each of the mechanical cleaners listed in Types, so you’re never forced to resort to a bottle of chemical goop purchased in a panic from the corner store.

If the sink backs up quickly. Chances are the clog is just below the drain or in the trap. In the kitchen, first pour boiling water down the drain to help melt away greasy blockages. Just take care to pour the hot liquid right into the drain or you risk cracking a porcelain sink. In the bathroom, hair is often the culprit. One product we tested, a 2-foot-long, toothed plastic strip called the Zip-It ($3), doesn’t have the range to snag deep clogs, but it’s perfect for fishing things like hair and dental floss from the drain just past where fingers can easily reach.

Prepare to plunge. Before employing a plunger, stuff a wet rag into any overflow drains and, if you have a double basin, neighboring sink drains. That way the pressure will be directed at the clog. Then fill the sink to above the lip of the plunger, so that you’ll force water, not air, at the clog. Finally, vigorously push and pull the plunger until the clog is forced free.

Use force on stubborn clogs. If the plunger doesn’t do it, or if using a plunger is too taxing, consider one of the products that use compressed gas or water pressure to pop clogs free. As with plungers, it’s critical that the mouth of the device be sealed against the mouth of the drain so that pressure is directed toward the clog and not back out toward you.

If multiple fixtures are clogged. The problem likely lies farther down the line, beyond the sink trap. Chemical drain cleaners typically won’t reach deep clogs in sufficient quantity to dissolve them. Instead thread a snake, also known as an auger, a long, steel, corkscrew-tipped cable, through the drain to bust through blockages, following the manufacturer’s directions. Because many sinks have a permanent strainer holder installed in the drain hole, you might need to unscrew and remove the J-shaped trap underneath the sink to get access to the drain pipe. Some traps have a square or hexagonal-headed clean-out plug that makes access a little easier. Either way, have a bucket on hand to catch the water and gunk that will drain from the sink. Ridgid’s Auto-Spin powered snake feeds and withdraws the cable at the touch of a foot pedal, leaving one hand free to, say, hold a flashlight. But it’s the priciest tool we tested.

Call a pro when mechanicals fail. If plunger thrusts, bursts of gas and water, and several twists of a snake don’t clear things up, the clog is probably deep in your main drain or in the connection to the street. Contact a licensed plumber or professional ­drain-cleaning service. Be sure to tell them what you’ve already tried, and if you’ve used chemical cleaners.

Keep drains clear. To maintain a free-flowing kitchen drain, don’t pour cooking oil, grease, or other fats down it. Transfer them to a jar, refrigerate the jar to harden the grease, and toss it all out with the trash. Don’t dump clumping foodstuffs like rice and coffee grounds in drains, either. Outfit all sinks with strainers to catch food, fibers, and hair, and clean them out often. Finally, flush the drain regularly with a few gallons of boiling water, which can melt away built-up grease and soap.