Gravity aided Catchment tank?

[Nate SC]

I see the concept basically working but the few concerns I have are once you start cutting into a intermodel container you lose structural integrity. You might have to tack weld a steel, RHS box into place under the water container for support. I see the best of both worlds with a two tank set up. The two stage collection would allow for increased capacity with a smaller footprint on the property and you could flush %50 of your water at a time without having zero water at any time. The primary collection tank being on the ground and fed from the rooftop gutters, in the area of maybe 5K Gal.? Then the secondary tank set on top of the container of about the same size or larger, maybe built on a platform. The primary ground tank would collect all run-off and would allow for a "first screening" of the run off. It would be best to have this be the larger of the two tanks. You could have a clean-out hole and a drain with a spigot installed on each tank. You could also have it piped with a 3" pipe for fire hoses. Water would then be pumped from the ground tank to the secondary holding tank on top of the container for holding. The pump could be a simple solar/wind pump(passive). The roof top holding tank in theory would be about 15' in the air and would dispense water for use. The water could be filtered at this point on the rootop or at the tap. You could also use black PVC arranged in a tight "S" patern on the roof to heat the water then send it to the tap using solar rays. The black PVC could also circulate thru a conventional electric water heater. An active/ on demand pump could be used to increase pressure at the rooftop tank as well. Using the formula presented here thats about 7.5 psi of water pressure(passive), give or take. That can't be right. Thats not including the volume of water put under pressure though? If it does work out to 7.5psi thats kinda weak for household use but more than good for irrigation. Upgrade the system to an active pump and it would be a kick ass system. Add a 2" 3gph pump and you could have a decent shot at fighting a fire until the pro's get there as well
Just been thinking about it for a while.
I've decided to convert a 20 ft container into a cabin/ storage box so I've been thinking about ways to trick it out. I plan on pouring four corner concrete post made of (2) 2X10's made into a box and then stacked one on the other as a form. I want to elevate the container off the ground for accesto the underside.