I am finishing my basement and putting in a half bathroom. I have PEX plumbing for the entire house (manifold is on other side of basement half bath wall). I also have superior walls in the basement with the preformed holes in the studs.
My questions are;
1) is it "legal" and OK to run two 1/2" PEX lines through a single hole in the stud?
2) Does the toilet need to be on a cold supply line than the sink?
1) I'm sure it's "legal", but it's not OK. When the hot and cold water lines share the same holes, the heat from the hot pipe will transfer to the cold line (after you shut them off and the water is just sitting in the lines). When the next user turns the cold tap on, the water will come out warm or even hot for a few seconds before the cold water forces it all out of the line. It's also advisable (even in the basement) to keep the water lines out of the exterior walls. Running them through the ceiling joists is a better option.
2) the toilet supply can tee off the line that feeds the sink.