tarred with the same brush, to be

tarred with the same brush, to be

Characterized by the same faults or bad qualities. This expression probably comes from sheepherding, where it was long the practice to treat a sheep’s sores by applying a brush dipped in tar. Since presumably all the sheep in one flock would be treated in this way, the term was transferred to humans sharing the same qualities. The figurative use dates from the early nineteenth century. In print Sir Walter Scott used it in several novels. John Ciardi, however, believed it came from the practice of sailors working with tar brushes (for caulking), and, being in cramped quarters, often tarring one another. This origin seems less likely.
See also: same, tar