I have about half a dozen quality bibs that I wear on rotation. When I've gone through 3 or 4 of them I wash them together as a separate load with the rest of my cycling kit on a sports wash cycle (30 degC, no softener etc). As for brands I have a mix of Assos, Rapha and Le Col and they all seem to hold up well to regular machine washing. I don't tumble dry them, just hang to dry overnight. I always have a couple of clean pairs ready to go