Jon Elson writes:

The license apparently gives you the option of building
your own system, so I did.

I believe you're required to have a recovery apparatus from a list of
approved commercial models. I squeaked by with buying one of the last
of the "Roger Ram" hand-pump versions back in the 1990s when they were
legal, which cost only $100s instead of $1000s for the cart systems. I
would dutifully use that to laboriously pump out the vapor into a
recovery tank that looks like a 20 lb propane tank, when I have R12
systems to work on. Not something you want to do every day.

I am not aware that you are allowed to roll your own in this regard. If
that were the case, I'd suggest a recovery tank in an ice bath.

I went to one of those closed-shop A/C
supply outfits, and they had the cap for something like $4.77
but didn't want to sell it to me until I showed them the EPA
green card!

Worth your while to lay in spare capacitors and contactors from eBay
instead of paying desperate retail prices. Or at least have Grainger
standing by.