Symptoms of a Sewer Drain Clog

symptoms of a sewer drain clog

Illustration: © The Spruce, 2018

A sewer drain clog is a very serious problem that can be considered a plumbing emergency and a potential health concern. Since the wastewater has no place to go, it will all come back up into the household plumbing system in one way or another. When you have a sewer drain clog, you should not use any of the plumbing in the home until the stoppage is cleared.


Watch Now: Symptoms of a Sewer Drain Clog

Sewer Drain Basics

Homes with city sewer service have a single sewer drain pipe running underground from the house to the street. The drain pipe is usually 4 inches in diameter but can be as small as 3 inches. The sewer drain pipe under the yard is connected to a main drain inside the house. Each plumbing fixture, including sinks, tubs, showers, and toilets as well as the washing machine, has its own drain that leads to the main drain. If the main drain is clogged, it eventually backs up all of the drains in the house. That's why a sewer drain clog is so serious.

Multiple Fixtures Are Clogged

An obvious sign of a sewer drain clog is when more than one plumbing fixture backs up at the same time. Toilets are often the first fixture to experience problems, but any other fixture can also be involved. If you suspect that you have a sewer drain clog, start by checking the toilet followed by other fixtures in the home.

Unusual Reactions When Using Fixtures

Check for odd sounds or behavior at the following fixtures, starting at the lowest level of the house. Sewer drains usually clog between the house and the street, and backups start at the clog and move up, so the lowest drains and fixtures are usually the first to back up.

  • Toilets: Toilets have the most direct path to the main drain and use the biggest drains of all of the fixtures, so this is where problems tend to appear first. You may notice that a toilet doesn't flush properly, or that the toilet gurgles when water is running down sink, tub, or washing machine drains. This is a telltale sign of a main drain problem.
  • Tub and shower: Other drains typically affected by a main line stoppage are those in the tub and shower. This is due to the fact that they sit at a lower level than sink drains. Check whether the tub and shower drains are blocked if you suspect a sewer drain clog. Showers and tubs may also fill with wastewater when there's a significant backup.
  • Run the sink: Another strange reaction to look for is trapped air in the plumbing system. If you run water in a sink—especially the sink closest to the toilet—you may hear the toilet gurgle or see the water level in the toilet rising. 
  • Washing machine: An unexpected sign of a sewer drain clog can happen when you run the washing machine. If the water draining out of the washing machine causes the toilet to overflow or backs up into the tub or shower, it's a good sign the sewer drain is clogged. Note: This symptom can just be a washing machine and shower problem and not a sewer drain clog. If the toilets are still flushing fine while this occurs, the problem is likely due to a washing machine stoppage and not a main drain.

    Checking a Cleanout—With Care

    A cleanout is a special fitting or a short pipe attached to a drain pipe. It has a round threaded plug with a square, nut-like stub on the end. Grabbing the nut with pliers or a pipe wrench allows you to turn and remove the plug to access the inside of the pipe. Most homes have at least one cleanout on their main drain or main sewer line. They are usually located in the basement or crawlspace or in the yard.

    Before you go any further: Do not remove the plug on a cleanout in the basement or crawlspace. If your main drain is backed up into the house, there may be a lot of wastewater—and pressure—in the pipe; anything above the cleanout will come out of the cleanout as soon as it's opened.

    If your cleanout is in the yard, you can attempt to remove the plug, but be careful. If water oozes out while you're loosening the plug, tighten the plug and call a plumber or drain specialist. If you can remove the plug without a spillover, look into the drain with a flashlight; any water in the pipe indicates a clog in the main sewer line.

    What to Do If Your Sewer Drain Is Clogged

    Don't run the water or flush the toilet! If you don't add water to your drain system, you can't make the problem worse (that is, if the clog is in your line and not the city's main; see below). As an added precaution, you can shut off the main water supply to the house so that no one runs the water by accident. Tell everyone in the house not to use water, then call a plumber or drain specialist to have the drain cleared.

    How Do I Know It's Not a City Backup?

    Your home's sewer drain connects to the city main under the street. If your house drain is backed up, chances are the clog is in your line, but it's possible the city main is backed up instead. Either way, your house drains will behave about the same, although sometimes city backups have enough pressure to force sewage into home drains, flooding bathrooms and creating other yucky problems.

    The best way to tell whether it's you or the city is to check with your close neighbors on both sides of your house. If one of them also has a backup, it's time to call the city. If city workers come out to investigate, they will repair only problems with the main sewer line; they won't take care of your line from the main to your house.