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Side Sewers and Storms

Your home's side sewer runs from the house to the main sewer in the street. Blockages or flooding of the side sewer can cause sewer backups. Maintaining the side sewer is the owner's responsibility. In preparation for storm season, maintenance is more important than ever.

The two I’s

Winter storms overload the sanitary sewer system in areas where there is excessive inflow and infiltration into the system (I&I). Inflow comes from stormwater connections to the sanitary sewer through roof gutters, sump pumps, yard or area drains. Infiltration comes from groundwater entering the sanitary sewer through cracks or otherwise defective pipes. The primarily source of I&I is from side sewers. If a side sewer is in good shape structurally, the likelihood of system overflows decreases.

What you should do with your side sewer before the storm season

  • Know where your side sewer line is. Make sure roots or other obstructions aren’t blocking or penetrating it. Remove trees that endanger it.
  • Avoid dumping fats, oils and grease down your drains, as they are the main cause of blockages. Instead, dispose of them in a sealed container in your garbage.
  • Make sure your side sewer is clean. If it is clean and there is a backup, we will know it was not caused by the side sewer and it will be easier to identify the cause of capacity issues in our system. If side sewers are not cleaned and there is a backup, the side sewer will need to be inspected by the homeowner before we can inspect our system, and we’ll have to make a decision on whether the primary cause is the side sewer or our system. All of this means it will take longer to fix the backup.

    Also, sewer backups make up a large percentage of calls to our emergency responders, leaving them with less time to deal with other more critical issues. If folks keep their side sewers clean, emergency lines are freed up during critical times like storm season.
  • If you need repairs to your side sewer, look under "Plumbing, Drains and Sewer Cleaning" in The Yellow Pages.
  • For more information about side sewers, see Your Property’s Side Sewer.

If you have a backup

  • Clean Up the Backup (pdf) is SPU’s guide to safe clean up.
  • Turn off all power to eliminate electrical hazards.
  • Keep children and pets away from the area.
  • If there is a heavy storm and sewage backs up through sinks or toilets, call Seattle Public Utilities' sewer and drainage maintenance staff at (206) 386-1800. City workers will check and remove blockages in the main sewer line. If the problem is the result of too much storm water in the system, you may have to wait until the storm has subsided to have the backup resolved.
  • Thoroughly clean the contaminated area. Use rubber gloves and disinfectants.
  • Discard saturated wall-to-wall carpet and pad; clean all hard surfaces with hot water and soap, then rinse with a bleach solution of one tablespoon of household bleach to one gallon of water.
  • Call Public Health-Seattle and King County for more detailed information at (206) 296-4632.