The process of removing sludge and scale from the inside of a locomotive boiler. The boiler was first emptied of steam and the hot water drained off. Water was then hosed into the boiler through 'washout plugs' while long rods were inserted into the plug holes to remove scale from the interior surfaces. After cleaning, the boiler was inspected for defects. Washouts used to be needed on a weekly basis for many locomotives but varied according to the age of the locomotive, the design of the boiler, its usage and the type of water used.