Ground Zero - S4-E14
Other mistake: When Hawke blows up Yahara's plane, we see that the video feed in the holding cell where Locke, Santini, and Rivers are is actually from a 3rd person perspective and that it continues, but according to previous dialogue (and video up to that point) the camera was installed on the plane, so once Hawke blew the plane up, there should have been no more video feed. (00:40:35)
Answer: No truth serum has proven to make a person tell the truth. Regarding capturing Mace, and forcing him to tell him where St. John is by water boarding him, People subject to torment such as water boarding are not likely to tell the truth, so Mace would probably lie.