That is one way... but you can just put the right amount into the compressor and each of the items you have off after you have flushed.... and when replacing just one item... like the R/D then you measure the amount which was in the old one.. and put brand new, newly opened , correct type oil into the new one, which is kept closed until the very last second...

PS, one of the things engineers like about the Delco 4 is that it can be run in any position..... It can do this because it HAS NO Chamber for holding oil.. it is lubed only by the oil flowing with the refrigerant....
The Yorks can only be run in two positions...
I do not know about the other rotaries.. but suspect they must be horizontal...