Haven't had time to read everything to see if this has been said yet but if the house has been abandoned for 2 years, and probably can assume the cistern has been undisturbed for longer than that then I would think it would be obvious if someone has had contact with it. Grass and weeds crushed down, dust disturbed, cobwebs down etc. With all the effort (and expense) this is taking I would think that if it appeared no one had been near there, under the deck, touching the cistern, then they wouldn't bother with this. I have to think that there were things that were "out of place" that led them to believe someone has been under this deck recently. MOO