ether...your joking right? haha.
put the mice in a cage or trashcan or something, put in some dry ice (blocked off so the mice cant get to it) let it let off some CO2 for a while. put in the mice with the co2 and seal the top. suran rap would work. they should all be dead in about a minute. i wouldnt want to have to take the time to wack 30 mice into a wall...
as for toxic stuff....i dont risk it. if it seems toxic, i dont get it near the snakes.