My local nano where I help out uses PBW in the keg washer. You invert the keg, then blow the cleaning solutions up the spear, and drain out the CO2 port.
Invert, PBW recirculate, blow it out, hot water rinse, blow it out, repeat rinse, blow it out, SaniClean recirculate, CO2 blow it out, repressurize with CO2.