First time listener, love the podcast.
I started Ice Baths when training for my first marathon the infamous 2007 Chicago Marathon Meltdown, and yes... I finished.
My routine is:
Get in the empty tub with my running shorts on, and a warm hoody on my top.
While sitting in the tub, empty the ice into the tub, and start filling the tub with cool water.
By the time the water is over your waist you've been in for 5-10min. and can either get out, or stay in a few more minutes. I find this is less of a shock to your body, than if you jump into a full tub.