I've never heard of the soap thing!!!
it does sound like a myth!
I hardly get leg cramps, but boy, I sure did get them bad when I was pregnant. I feel you pain!! My doctor gave me an info sheet about them, I dug that up and I'll give you the gist of what it says:
Causes: Medications, heavy fatigue, new exercises, dehydration, high weight, and electrolyte imbalance.
Long term Remedies: Stay hydrated, stretch regularly, train gradually.
Short term Remedies: Massage the cramped muscle, gently stretch the muscle, hot shower or bath to relax the muscle.
I'd keep up the walking. Just take something for the pain, drink a Gatorade, go for your walk, and take a hot shower when you get home. Not going to lie, that actually sounds pretty fabulous.