Soaking to me means wetting thoroughly (sink, shower, bath, bucket…) Always wash inside out, and I use liquid detergent. I’ve not had any problems following those steps.
They really need to be wet (and inside out) before they hit the washing machine….
Your washing machine may have a soak setting where it will handle that stage before it gets going.
Ended up drenching my pair under a shower before washing machine. Used just normal detergent on a 40c eco program. Came out fine, no trace of marbling or other unwanted blemishes.