Substrate liquid treatment apparatus, tank cleaning method and non-transitory storage medium

A tank cleaning method executed in a substrate liquid treatment apparatus, the substrate liquid treatment apparatus including a tank that stores a processing liquid, a circulation line connected to the tank, through which circulation line a circulation flow of the processing liquid that leaves the tank and then returns back to the tank flows, a distribution line branched from the circulation line at a first branch point for supplying processing liquid to a processing unit, wherein the processing unit processes a substrate by supplying the processing liquid, distributed from the circulation line, to the substrate via the distribution line, a return line that returns, to the tank, the processing liquid discharged from the processing unit after being supplied to the substrate, the tank cleaning method comprising:

• extracting the processing liquid flowing through the circulation line at a second branch point downstream from the first branch point to a cleaning line;
• discharging, as a cleaning liquid, the processing liquid from the cleaning line to a cleaning nozzle onto an inner wall surface of the tank, thereby cleaning the inner wall surface by the cleaning liquid;
• and
• regulating the pressure in the distribution line by adjusting a constant pressure valve located in the circulation line between the branch points.