Garbage disposal causes water to back up into the opposite sink basin in a double sink configuration.

Safety first: Turn off the disposal and do not run it while water is backing up.

• Check the baffle tee: Under the sink, inspect the tee fitting connecting both basins. Ensure it is oriented correctly and not blocked.
• Clean cross-over pipe: Remove and clean the horizontal pipe between the non-disposal sink and the disposal side. Clear any food or grease buildup.
• Snake the drain: If both sides back up, use a drain snake from the wall stub-out to clear deeper obstructions.
• Run water while grinding: Always run a strong flow of cold water while using the disposal to help carry waste through the shared drain.

If backups continue despite clear piping, the main kitchen drain line may be undersized or partially blocked and a plumber should evaluate.