How to remove pipe sealed with silicone
You don't remove it.  The silicone is probably just to secure the pipe to the wall - so it doesn't wiggle or so that air doesn't get in.  

If you need access to the pipe I would cut the white pipe.  This would allow you to fully snake anything below.  Chances are pretty high that all of these pipes are glued very well together.  They are not meant to wiggle apart.  If you do not want to cut them then you can try putting in a snake from a point further up or you can see if you have access from below in your main stack.