So what I did after replacing my PCV valve, I didn't drain the whole coolant system but did get a fair bit out. Filled the resevoir and cracked the bleeder screws on the S/C. Heater on high with fan as low as it could go to get the thermostat open. Ran the engine til it warmed up, bled through both S/C screws and then the heater core hose. Had a partner run the engine at 2000rpm while doing so.

Refilled reservoir a time or two during this process, then took it for a drive. Took a couple drives around town in sport mode over a couple days to keep the motor over 2000, then let the engine cool off and topped up the coolant reservoir. Good to go now, level hasn't dropped and have good heat.