wrote in message

My point is that as soon as
I can find the proper adaptors, I am going to fill all of my old 20lb
tanks FROM my 500 gallon tank. It will even be cheaper than having
them filled, and because they got the old valves, no one else is
allowed to fill them.

Anyone know where to get the proper adaptors? (I got the end for the
20lb tanks).

I think you need more than just the fittings. Propane is pumped under
pressure to fill the tanks. I don't know the details, but AFAIK, this is
not a simple DIY thing. It is a liquid inside the tank and must be filled
off the bottom of the big tank as the top would be a gas. Investigate more
before you spend any money.
Ed