Fill a large soup pot with 1/2 gallon of white household vinegar. Put it over high heat on the stove and bring the vinegar to a boil.
Lower the dirty paintbrushes bristle-first into the boiling vinegar and remove the pot from the heat. Let the paintbrushes sit overnight, then rinse them in clean water from the tap.
Fill the sink with warm water and add enough liquid dish soap to create suds. Lower the paintbrushes into the soapy warm water and use your fingers to pull off any remaining paint. Rinse the brushes clean in the tap.
Lay the brushes out to dry on a clean towel overnight.