Abstract: A low profile holding tank-evacuable to a pressure differential of at least about 10? of mercury that includes a plurality of support structures, a peripheral wall, an upper outer layer of mild steel and a lower outer layer of mild steel, each of the upper outer layer and the lower outer layer is configured to be up to about ¼ inches thick. At least some of the plurality of support structures are required to be fixedly connected to upper and lower outer layers to prevent damages incurred on the low profile holding tank by repeated applications of the pressure differential of at least about 10? of mercury. At least some of the connections are required to be made from the outside of the tank via a welding, e.g., plug welding, technique.