How Do I Unblock A Washing Machine Waste Pipe Updated May 2026

| Symptom | Likely Locus | Physical Mechanism | |--------|--------------|---------------------| | Water backs up into sink when machine drains | Downstream of sink branch (shared pipe) | Constriction raises upstream pressure | | Water spills from standpipe top | Blockage in trap or horizontal run | Pump head exceeds standpipe height | | Machine drains very slowly (over 5+ mins) | Partial occlusion in hose or standpipe | Increased viscous pressure drop (Hagen-Poiseuille: ΔP ∝ 1/r⁴) | | Machine won’t drain at all, pump hums | Pump filter or hose inlet blocked | Solid object (coin, hairpin, bra wire) |