Tank bottoms are normally sloped approximately half an inch per foot of tank diameter from the high side to the low side. They are used for non pressure /non vacuum applications and can be equipped for complete drainage with internally flush center drains. The insulation between the two tank bottoms is of cylindrical perlite. They are cleaned periodically by circulating accumulated method. All tank inlet and outlet connections, mixing devices and water draw-off connections are located beneath the level of the tank bottom. The tank-cleaning process can reduce hazardous waste generated from tank bottoms.