We are looking at an 60-70 year old rural house that we might buy . Out in the back yard is a good sized metal tube [@18-24" dia.] sticking straight up about a foot with a slightly rusted through lid that is equipped to be padlocked . I have not yet looked into this thing . I don't think it's a bomb shelter as there should be vents some where near and the tube doesn't look big enough to climb down . There are two things I think it might be : an old cesspool [maybe a septic tank ?] or an old buried propane tank . I know what I would see if it is a propane tank . If it is a cesspool or septic tank , I presume I would see and probably smell [yes , I know to let it ventilate before looking inside] human waste-does anyone know if there is any visual difference likely between the two that would be visible from such an access point ? I will be contacting the real estate agent before/if we decide to take another look but I want to be prepared to try to figure it out myself if need be . Sorry , I don't have any pictures . I have searched the internet and cannot find anything that looks like this . Thanks for any ideas .