I soaked in RO for a couple weeks, and changed the water out every couple days. I was half-heartedly looking for a container to house them which took me a couple weeks, so I did the rinsing simply because I could. Siporax is glass, so really the only thing it could leech is silica. Here's a thread discussing it with Randy Holmes-Farley.
http://www.reef2reef.com/threads/doe...silica.267161/