Well I've never been told you have to warn for a T trap and there is nothing in the rules saying you have to. Since it isn't common sense, and all servers are different, it really should be written in the MOTD that you need to warn for things like poisoning the water in that one terrible Minecraft map and stuff. I was slain for two rounds for killing two T's with the poison water and it doesn't say anywhere that you have to warn. There are obvious signs that the water is poisoned, so it shouldn't be slayable.
There's only one rule for traitors, and that's no killing traitor buddies. You need to warn before throwing a traitorous grenade, Jihading, activating most traitor traps, etc, beacuse if you don't and you kill a traitor buddy, then you will be slain.
Also, "There is a fair amount of time between the button press and actual poison. The poison only triggers after the entire cave shakes, after the Rock has fallen/bridge destroyed, and only JUST after the pulsing lights and ambient warning sirens kick in"- @Books. There is actually plenty of warning time for any traitors to leave the water before it's poisoned, so no warning is actually required for activating the poison T-trap on Mythic.
Yes. As Mango said just above me, slay records are not something to worry about. They are so minuscule in-fact, that we actually went through and deleted thousands of Notes on player records that mentioned slays. This is because said records take up valuable space, and serve no actual applicable use. Rest assured, Event will take care of it on our end.