A dual tank structure includes first and second tanks with a common secondary containment structure which are all integrally supported on a common base frame. The common base frame includes longitudinal skids so as to be suitable for transport using a conventional winch truck. A passageway with an integral valve therein permits selective communication between the tanks. The common containment structure has a containment volume which is greater than a storage volume of a largest one of the first tank and the second tank and which is less than a combined storage volume of both the first tank and the second tank.

An apparatus and method for cleaning the interior of an above ground storage tank includes a nozzle assembly mounted to a cover on the storage tank sidewall having a horizontally extending wash pipe fixedly and a suction pipe for recirculation of spent fluids. The wash pipe has an interior segment which can be extended to a tank floor and is configured with a bend to extend along the tank sides all to which is attached a submersible swivel joint fitted with a choked nozzle. A control assembly is provided to direct from the nozzle from the exterior of the storage tank. The nozzle vibrates in response to flow of wash fluid from the wash pipe.

A method for maintaining solids and heavy liquids in fluid suspension within a bulk storage tank includes providing a nozzle and suction assembly mounted to a storage tank sidewall having a horizontally extending discharge pipe and a suction pipe for recirculation of the emulsion of fluids within the storage tank. The discharge pipe and suction pipe can be extended to the tank floor and configured with a bend to extend along the tank sidewall to which is attached a submersible swivel joint fitted with a choked nozzle. The nozzle and suction assembly produce positive and vacuum pressure, respectively, for causing the simultaneous discharge and suction of contained tank fluids to cause recirculation. The nozzle may be adjusted so the direction of flow may follow the angle of the tank floor.

An apparatus and method for cleaning the interior of an above ground storage tank includes a nozzle assembly mounted to a cover on the storage tank sidewall having a horizontally extending wash pipe fixedly and a suction pipe for recirculation of spent fluids. The wash pipe has an interior segment which can be extended to a tank floor and is configured with a bend to extend along the tank sidewall to which is attached a submersible swivel joint fitted with a choked nozzle. The nozzle assembly is attached to a control assembly so that the direction of flow from the nozzle may be manipulated by rotation of the swivel joint from the exterior of the storage tank. The nozzle also may be adjusted so the direction of flow may follow the angle of the tank floor.