A kitchen or bathroom sink that gurgles or backs up when your washing machine discharges wastewater points to a partial blockage or venting issue in the main branch drain line. Because washing machines pump out large volumes of water rapidly, a partially restricted pipe downstream cannot handle the high flow rate. This forces air to compress and bubble up through nearby sink P-traps, creating loud gurgling noises. Verification: Inspect the main laundry drain line and clear any accumulated lint or soap residue.
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