I created a guide for creating a purge line for every toolhead. I did this because I had a few instances where the prime tower fell over due to poor adhesion on the first layer because the toolhead wasn’t primed.
Under multimaterial, (prime all printing toolheads) that are being used for current job.
I just tried that option and it seems like the printer primes every toolhead before the toolhead is used in the printing. This contrasts with priming the toolhead only when that toolhead is required.