Ten-yearly: confirm the shorter-interval activities were completed; drain and clean the tank completely (remove sludge and debris, low pressure spray all internal surfaces except the roof, refill promptly), or for lined tanks leave at least 50 mm of water and avoid damage to the liner, positioning the liner and any neoprene mat under the vortex inhibitor before refilling; divers or other underwater techniques may replace draining with the manufacturer's agreement. Pressure tanks receive a six-yearly internal inspection by a pressure vessel inspector qualified for the work.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.