500 gallon Propane tank for Pressure Tank

My neighbor has been using, for some time, a 500 gal. propane tank for a pressure tank.
I am interested in doing so to keep my pump from cycling.
My neighbor states that his submersible pump will run for about 2 hours to fill the tank. After that, he has water for quite some time before it kicks on again.
Does anyone see any drawbacks to doing so??

Instructions I have been given:
Clean inside of tank thoroughly with hot water and bleach.
Remove fittings from tank and plug holes.
Paint tank with oil base paint. Paint tank with tar.
Bury the tank in the ground with the top of the tank at the water line level.
Connect "filler" port on the tank to the water line and the pressure switch.
Place an air filling means to the "gas" port on the tank.
Construct a manhole to the tank ports.( 5 gal. bucket with the bottom cut out placed over the ports)
Fill tank approximately 1/4 full with water.(Remove a plug and check with a stick.)
Add air pressure to 2 lbs. under cutoff.

Why not buy a tank designed and made for potable water? I installed a buried 300 gallon John Wood last summer, it was very reasonably priced and I had no contamination worries.

What is reasonably priced?

Since a 500 gallon pressure tank with the proper air charge only holds about 150 gallons of water, and it takes two hours to fill, I am guessing this is only a 10 GPM pump? Talk about overkill. That is like having a 6 car garage when the only vehicle you own is a little motorcycle.

Back when big pressure tanks where actually needed, a propane tank looked like a reasonable alternative. However, with all the extra fittings, and none of them in the right place for an air volume control, there are multiple places for air to leak out. Propane tanks are notorious for getting waterlogged.

With a bleeder orifice air injector system, the tank only gets a small charge of air each time the pump starts. One or two starts a day is nowhere near enough starts to keep the tank charged with air. Your only alternative is to regularly air the tank up manually with a compressor. I know you think you can remember to regularly air up the tank, but you can’t. You will forget. And forgetting just one time and letting the tank waterlog will cycle your pump to death before you remember you should have aired up the tank.

The inside of those tanks is not coated with anything, so rust in the water is also a big issue. Then with a 40/60 pressure switch setting, the pressure in the house will always be decreasing and will be on the low side for a long, long time.

We haven’t even discussed the expense and trouble to paint, plumb, and burry a monster tank like that.

Yes, long pump run times and reduced cycling are good things for the pump. But there are much better ways to eliminate cycling. A bladder style tank makes it maintenance free, as you never have to worry about the air charge getting out. Then when using a Cycle Stop Valve, the bladder tank can be as small as a 5 gallon bucket and the pump will not cycle at all while you are using water.

But don’t get me wrong. You can make a propane tank work with enough regular maintenance. Of course you can also go back to the fifties by getting a black and white TV, party line telephone, and by driving a Studebaker. If you are not old enough to know what any of that stuff is, then you need an old propane tank to use as a pressure tank. It will help you understand the benefits of newer technology.