A bit late to the angel eye party: 2001 M5

[ViPER1313]

That might be necessary if you get the mixed stuff (to keep the oil / stop leak additives mixed / flowing out.) Been a while since I have done it. Flashing the coolant like that is fine; the bit of liquid that comes out when at 3oclock turns to vapor in the lines and by turning it back to 12 you are giving the compressor a chance to recover. You just don’t want to keep the bottle below 3 continuously unless you are using a liquid charge adapter (which is only really necessary for a blended coolant like 410a)

Yellow Jacket 41123 1/4 inch Liquid Charge Adapter, https://www.amazon.com/dp/B005DLBXWU/ref...6AbXQTHKTX