How Drain Cleaners Work

Clogged drains are a common household problem.
Clogged drains are a common household problem.

You know how it happens. You have guests coming over for dinner in a few hours, and you want everything to be perfect. You take the dirty pots out of the sink and open the strainer, but nothing happens. You search the top of the drain to see if something is blocking the water, but you can't find anything that can easily be removed. You're stuck with a sink full of murky gray water -- the drain is clogged.

There's no good time to lose the use of your kitchen sink or bathroom lavatory without warning, but a stopped-up drain is no reason to panic. Sometimes, simple measures can get things flowing again.


Commercial drain-cleaning products are one option that can be effective in certain circumstances. Some of these products are heavily advertised and their brand names are household words, so you may be tempted to pour them down a clogged drain before trying anything else. However, this may not be the best strategy. In many cases, there are alternatives to drain cleaners that will be more effective and less risky to your health and the environment -- and they may even cost less [source: Harrison].

Read on to learn how to clear clogged drains, how drain cleaners work and how to avoid the dreaded clogged drain.

Dealing With Clogs

Why do drains clog? The short answer is because of the way we use them. Obviously, even though it's not supposed to happen, water isn't the only thing going down most drains. In fact, knowing what has clogged your drain can be an important step in knowing how to clear the clog. At the kitchen sink, grease and small particles of food can make their way into the drain. In the bathroom, hair and soap scum are the biggest offenders. Over time, these substances can build up and begin to line the drain, and then one day, another piece of food or another clump of hair is all it takes to block the drain [source: Goodway].

Foreign objects, such as jewelry, bottle tops or toys, can also fall into a drain and clog it. If that's the case, drain cleaners won't help unblock the drain. You'll need to remove the object or call a plumber to do it for you.


Assuming your problem isn't a foreign object, first try to locate the clog. Start by removing, checking and cleaning the stopper or strainer at the entrance to the drain. Some strainers are easily removed by hand, but others may require a screwdriver or pliers. Remove anything you can reach and then try pouring hot water down the drain.

The next step is to try using a plunger on the drain, and if that doesn't work, try removing and cleaning the sink's trap. After that, you may want to try a sewer snake, or auger. If none of these efforts works, it's time to use a drain-cleaning product [source: Harrison]. Read on to learn the pros and cons of various drain cleaners.

Chemical Drain Cleaners

Chemical drain cleaners are one way to unclog sinks.
Chemical drain cleaners are one way to unclog sinks.

Be they liquid, gel or powder form, most of the drain cleaners you'll find on store shelves use strong chemicals, and they come in liquid, gel and powder forms. All chemical reactions involve moving electrons, and drain cleaners work by either taking or giving electrons to the clogging substance, generating heat in the process. There are three main types of drain cleaners:

  • Caustic drain cleaners contain substances such as lye and caustic potash. They're bases, so they give electrons to the clogging substance, and their hydroxide ions create the reaction that clears the clog. Their alkaline, or basic, chemicals release heat and turn grease into a soap-like substance that's more easily dissolved. These drain cleaners are typically heavier than water, which enables them to reach the clog through standing water.
  • Oxidizing drain cleaners contain substances such as household bleach, peroxides and nitrates. These chemicals cause the organic material of the clog to lose electrons and become oxidized. The product is heavier than water, so it can move through standing water, and it releases heat and gas to help clear the blockage.
  • Acid drain cleaners aren't commonly found in stores, and some are sold only to plumbers. These typically contain high concentrations of sulfuric acid or hydrochloric acid, substances that increase hydronium ions in a solution and attract electrons from the clog. The hydronium ions react chemically with the material in the clog, and the reaction releases heat, which is necessary to melt congealed grease [source: Sheridan].

Because most of these products generate heat, they may soften the polyvinyl chloride, or PVC, pipes found in homes today. However, such damage is rare if you use the drain cleaner as directed -- damage is more likely to occur when drain cleaner is used on older, metal pipes.


Aside from their effect on pipes, there are other disadvantages to chemical drain cleaners. They're extremely toxic if swallowed, and they can burn eyes, skin and mucous membranes and eat through clothing. They can release noxious fumes, and if used improperly, they can cause explosions. These products can also harm septic systems by killing beneficial bacteria, and they can mar bathroom and kitchen fixtures.

If you use chemical drain cleaners, read the directions carefully and heed all the warnings. Use the product in a well-ventilated area, wear rubber gloves, and keep children and pets away from the drain. Never mix different drain cleaners, and don't use a plunger in conjunction with drain cleaners.

Most drain cleaners advise waiting 15 minutes or more after pouring the product into the drain before flushing it with hot water. If your drain is still clogged afterward, you may need to repeat the process.

Read on to learn about alternative drain cleaners.

The Alternatives: "Green" Drain Cleaners and Do-It-Yourself

Enzymatic drain cleaners may be a safer alternative to chemical drain cleaners, and they're easier on the environment. They use bacteria or enzymes that naturally feed on organic waste materials, such as hair and food waste, that often clog drains [source: Green Home]. These tiny living organisms then digest the waste and reproduce, spreading beneficial bacteria and enzymes throughout the septic system [source: Sheridan]. In fact, enzymatic drain cleaners were originally used to clean septic tanks and wastewater systems. Enzymatic drain cleaners are better for the environment because they don't contain dangerous chemicals that can leak into soil and water.

However, these drain cleaners do have their disadvantages. They're not as readily available in stores, and they work more slowly than chemical cleaners -- clearing a clogged drain may take hours. These products also tend to have a shorter shelf life than chemical drain cleaners do [source: Sheridan]. And although they're not as toxic as chemical products, you should still take the same precautions as you would with chemical drain cleaners.


If you're the do-it-yourself type, there are also some simple home remedies for clogged drains, including:

  • Pour half a cup of baking soda down the drain. Then pour half a cup of vinegar. Wait 15 minutes, and then pour in hot tap water.
  • Mix equal parts salt, vinegar and baking soda. Pour into the drain. Wait one hour, and then pour in hot water.
  • Mix half a cup of salt and half a cup of baking soda, sprinkle it into drain and then flush with hot water [source: Harrison].

There are a variety of remedies that may break up the clog in your drain, but wouldn't it be better to avoid clogs altogether? Read on for a few simple suggestions on how to prevent clogs.

Preventing Clogged Drains

Good habits and basic maintenance can help prevent those dreaded clogs. First, don't tempt fate by dumping food in the sink or pouring grease down the drain. Put food and coffee grounds in the trash, and let grease cool and then put it in a container and throw it away.

Keep sink strainers in place -- they're there for a reason -- and clean them frequently. If you have a garbage disposal, be sure to run cold water while you're grinding up food scraps. If you don't use enough water, you may encourage food particles to build up in the drain [source: Lowe's].


In the bathroom, remove the sink stopper and clean it often. Small screen covers, often available in stores, can help keep hair and other pesky materials out of drains. Don't flush paper towels or other heavy paper products down toilets.

Once a week, pour hot water down your drains to help dissolve grease, soap scum and other buildup before it clogs the pipes. If you have a home septic system, have it inspected every few years -- it may need pumping after several years.

For more information on drain cleaners and how to prevent clogs, see the links on the following page.

Lots More Information

Related HowStuffWorks Articles

  • Bioguard Plus. (Accessed July 14, 2009)
  • Drano. (Accessed July 7, 2009)
  • Goodway. "Drain Cleaner and Drain Cleaning." (Accessed July 14, 2009)
  • Green Home Environmental Store. (Accessed July 7, 2009)
  • Harrison, Mary N. "Making Simple Repairs: Clogged Drains." University of Florida IFAS Extension. (Accessed July 7, 2009)
  • Liquid-Plumr. (Accessed July 7, 2009)
  • Lowe's How-To Library. "Clearing Clogged Drains." (Accessed July 7, 2009)
  • Sheridan, William D. "Reference Data Sheet for Chemical and Enzymatic Drain Cleaners. Meridian Engineering & Technology. November 1994. (Accessed July 14, 2009)