A/C Evac does it matter?

I really think in the near future I will pull my engine to change the flex plate, "what a pain in the ass" and need to discharge the air conditioner system. Does it really matter if a guy just dumps it because it's r134 or is it necessary to go somewhere and have someone else evacuate it. Is it enviromentally irresponsible to just open it and let it fly or what? Any input on this really appreciated. If this was any other car I would get rid of it, but this SVX put some kind of spell on me so I will keep the nickles and dimes coming that it takes to keep the beast alive.