(materials a dairy farmer buys that are used to build a manure containment facility are subject to sales tax; Mo. Rev. Stat. Sec. 144.020.1 imposes sales tax on retails sales of tangible personal property and Sec. 144.030.2(15) exempts certain equipment and devices used solely for water pollution abatement; permanent structure on real estate does not qualify as "machinery, equipment, appliances or devices under the exemption; thus, materials used in construction are not exempt).