bbc!verse John and Sherlock trapped in a tank

[lynns118.livejournal.com]

Hi all,

I feel like this search has been done before but I've been searching in the bbc tags and couldn't find it.

I'm looking for a bbc fic where in one scene Sherlock and John wake up and find themselves in some sort of tank. Water starts filling the tank and they realize that John is actually chained to the bottom while Sherlock is not. Any help findings his fic would be appreciated. Thank you.