Standpipe Clog

• The standpipe is the vertical pipe that the hose from your washing machine dumps its waste water into. This pipe is intended to allow water from the washing machine to drain into the drain line while keeping sewer gas from flowing back into house. Standpipes can become clogged with lint and other debris removed from washed clothing. Use a plumber's snake to ream out as much of the standpipe and drain as you can, and see if the issue is resolved.
  
  

Drain Cleanout

• Drains can become clogged further down the drain line than a plumber's snake can reach when fed through a standpipe or sink drain. For this reason, most modern homes have a drain cleanout plug somewhere in their drain line. This plug can be removed, and a plumber's snake can be fed directly into the drain line. The plugs are typically located in the basement, crawlspace, or outside your home near the foundation.
  
  

Improper Ventilation

• All drains need to be vented to flow properly. Water passing through a drain creates a vacuum that can slow down the movement of waste. A drain vent keeps air moving and prevents vacuums from forming. If your laundry room drain is improperly vented, water may not continue beyond the drain. The drain creates a vacuum, and water leaks out into your home. Ensure that your entire drain line is vented properly and is up to local code.
  
  

Sewer Issues

• If your laundry room drain is the last drain in your home, an overflow may be indicative of a sewer problem. A collapsed sewer pipe, or one damaged by a tree root, would cause water to back up into the home and overflow the first drain it reached. Issues involving the sewer are not user-serviceable, and a professional plumber or drain service will need to be called to examine your sewer line.