I don't know what state you live in because you haven't filled in your profile, but don't believe that you can avoid the sales taxes for very long. It is hard to hide a tractor and things like this have a way of coming to the surface to the tax people. Most states have either a use tax in conjunction with the sales tax. Many states also have an excise or personal property tax on top of that, that goes to the town or county. If your neighbor is paying it on his tractor, you can almost bet that he wants to make sure that you pay it on your tractor. In CT you pay taxes on the head of cattle, chicken, horses, tractors, snowmobiles, cars, trucks, trailers, and any thing else that the town tax assessor can pin on you!!!! I believe that if they thought that they could get away with taxing your septic system as a fertilizer system, they would tax that also. Our neighbor to the East is known as Taxachusetts, but Connecticut has them beat hands down. Pay the sales taxes up front, it is less expensive than getting caught later on.