Kaopectate. I find Immodium too strong and likely to bind you up for a few days.

Also, don't run to the pot at the first signs of wanting to, try to hold it as long as possible, even while sitting on the pot. Every second counts and lets your body remove some of the water naturally.

If you start getting weak and can't eat. Try glucose and a little salt in water or juice to keep your strength up.