If I recall correctly, there was a recent issue on the ForgeCraft 2 server (commented on by Slowpoke101) that you could accidentally teleport into the 'interior' of a XyCraft Tank and you'd get smothered and killed in short order. Tank's contents would also get invalidated in the process. This bug has apparently been fixed, but hey.
On a funny note, you can bust some blocks out of a XyCraft Tank.. climb INTO it and then reform the tank from the inside by replacing the blocks and right clicking the BACK of the valves. The tank would form around you, but the liquid inside was REAL so you'd drown if it was full.