we use a brand called diversatech or something like that. You open a can like brake fluid can and pour into this special container. the container connects to nitrogen and the nitrogen generates the pressure. Then we purge with straight nitrogen.
The other day we installed a 5 ton Carrier and coil but forgot to flush the line set. It didn't want to work right at all. sub cooling 50 and super heat 50. Recovered all 410a, flushed like crazy the entire system, new dryer, 400 micron vac, weighted in charge and then everything was fine.