A cheap and relatively easy way to check verticallity of concrete slip form silos (as an example) during construction is to use a closed 55 gallon tank (or similar) with two, three or four long hoses connected to the tank. The tank and hoses are filled with water. Since the tank and hoses are (hopefully) a closed system, the water level in the hoses should be at the same elevation. So, as the slip form silo is constructed upward the hoses, which are placed around the slip form, are used to keep the slip form relatively vertical as construction progresses and subsequently the silo itself. While this method is a constrcution technique it might be useful as a "rough" check on the verticallity of your bulk storage tank. This is a technique that can be used "during" the construction or installation of your tank. Otherwise, a competent surveyor can establish the verticallity of your foundation prior to construction and a check of the tank after construction or installation.