by Why does my toilet gurgle when the washing machine drains?
Short Answer: The rapid laundry discharge is creating pressure changes in a restricted drainage system.
Detailed Answer: When wastewater flow is impeded, the surge from a washing machine can displace air through nearby fixtures, producing toilet gurgling. Septic restrictions, sewer-line blockages, and vent problems are common causes.
Related Questions: Can washing machines expose septic problems? What causes plumbing gurgling? How do I diagnose a septic blockage?