if you want something to stand up to better heat/cold temps use systesm 636 pvc or cpvc used for flue gas venting
not sure what the laws are in other provinces or states but in ontario it's a must so it's easily available (required to have a gas fitter license)
btw check here for immersion heaters
NOL have you tried to drill through hard materials with that hole saw? like dense LVLs, espanite, or sheet rock?