I appreciate your survival ideas over the years. Here, in the Caribbean, we use cisterns for water recovery quite a bit.
I’ve had occasion to make a cache lately from one of the smaller plastic cisterns, such as this one.
The tanks that come here (Cayman Islands) are black and configured somewhat differently, but same basic idea. They employ a screw-top opening, which can be weatherproofed against all but profound water pressure.
I set mine — a 750 gallon tank — in the sandy loam and made sure that the bottom third was all clean fill, especially under the tank. I bedded around the upper 2/3 with fairly large, but smooth rock, and concreted around the circular opening, so I could keep it clear of dirt and grit. I used thread-seal tape and teflon pipe sealant on the threads of the lid, and it’s watertight, at least until such time as it is completely underwater (future hurricane?).
I took a piece of 3-foot x 3-foot starboard (polyethylene) and cut it in an irregular shape, and glued sand and rock to it, such that when laid down over the opening, it appears uniform. I used polyethylene plastic rather than plywood, because it tends to not “echo” as badly when stepped upon.
Another idea that I’d like to mention: To prevent flour weevils in my stocked dry goods, I simply freeze each product (flour, pasta, beans, etc.) for 24-hours. That explodes the insect eggs, and they are good to go in preventing weevils after that.
Thanks again for all the time and effort. First time writing. Be safe. – B.L.