Quote Originally Posted by Maxion View Post
In the stomach, the dot that scales with spellpower is constant all over and the one from the acid is separate from it, if my memory serves me right.
http://www.wowhead.com/npc=15727

Stomach of C'thun: The stomach of C'Thun is an entirely separate room. Every 10 seconds, a tentacle will emerge and swallow a random person in the raid. You fall from the top of the new room into green water, and are given a stacking debuff called Digestive Acid, that reapplies itself about every 4 seconds, and can stack up to 99 times, doing 150 Nature damage every 5 seconds per application. There are two Flesh Tentacles in the stomach that must be killed to weaken C'Thun, causing its body to turn purple and become vulnerable to the attacking raid for 45 seconds.

That's the only DoT you get inside the stomach, but scales with SP instead of just doing 150 per application.