It screws onto the tank, in between regulator and tank, this goes inline, no need to empty the tank, just shut the valve. You might want to burn off what’s left in the line after the regulator before you unscrew it to install this. Shut off the tank valve, burn off excess at your stove and/or heater till it peters out.
If you’ve got a suburban heater, it might take a few extra minutes to light until gas fills and pressurizes the line. You do need to buy yourself a few inches to fit this in, like I said, I was able to sneak my tank forward? and I moved the copper line a bit to fit it in, careful not to put a kink in it. Not that difficult, just takes a bit of time and care. Or you could always have an RV dealer or shop install. There’s a few different versions, make sure to order or get which one has the right fittings. Example….