I'm in Virginia, in the county in the country.
Here a homeowner basically can do anything he/she wants.
I just looked this up for Connecticut...
"The tank would have to be installed by a person licensed to do this work in Connecticut, e.g., a master plumber."
Over the years I've done lots of things not to code, but common sense

. Sometimes getting a license, inspections, etc. opens a can of worms.
I buy my propane from the place I bought the tank and get a really good price. They do a leak down test which is a gauge on the line, open then close main tank valve. If it holds that pressure 24 hours all is well.
Me, I use soapy water and small brush (or a match

...joking!).