Treehouse at Menangle NSW

For years I have wondered about the house on slits beside the Hume Highway, between Sydney and Canberra. On this trip I noted it was near the Nepean River bridge. So I looked on Google Maps, but could not see a structure. A web search found "Getting tanked" by Tim the Yowie Man (Jul 7 2012), who reports the structure is a water tank. This is surprising as it looks like a house, with a pitched roof. An alternative explanation from the Border mail ("The Smoking Gun", Nov. 16, 2012), is that it was originally a tobacco drying facility.