You should be able to tilt the mash tun an collect all but maybe a quart or so. IMO, it's best to allow for some losses when formulating your recipe and don't stress about grabbing every last drop of wort. It's just not worth it. I fly sparge, so most of the time what is left behind contains almost no sugar anyway. I can see wanting to get as much out of the MT as possible when batch sparging, but I would not go to much trouble to do so when just adding a pound or so of extra malt to the recipe is often enough to cover minor losses.
BTW, you might want to switch to cpvc rather than us the pvc. The cpvc is designed for higher temperatures and I'm in doubt about the safety of using regular pvc in this application.