All the closed top tanks listed below are cylindrical, with integral tops. All the tops have a screw-on fill port, the cover/hole size is listed. Tanks can be ordered with a bulkhead fitting at the bottom, but it must be requested with order. Plumbing parts, for instance, nipples and valves are not supplied unless ordered separately. Bulkhead fitting sizes vary with the size of the tanks. All the closed top tanks can also be used as secondary containment vessels by cutting off the tops, which can be easily done with a carpenters handsaw or power tools.