Unclog a washing machine drain by first removing the drain hose and checking for lint and debris buildup. Clean the hose with a long brush or by flushing with hot water. The standpipe drain often clogs where the hose enters. Use a drain snake inserted into the standpipe to clear the blockage. Pour baking soda and vinegar into the drain followed by boiling water. Install a lint trap on the drain hose to prevent future clogs.