Pour 1/2 cup of baking soda followed by 1/2 cup of white vinegar down the standpipe. Let it fizz for 15–30 minutes to break down grime, then flush with a gallon of boiling water.
Best for slow drains caused by soap scum or grease buildup. Do not use this method if pipes are PVC/Plastic and you suspect they are cold/fragile; use hot tap water instead. how to unclog laundry drain
Before starting, determine if the issue is in the washing machine itself or the house plumbing. Pour 1/2 cup of baking soda followed by