Depends on whether you breath in and breath into the pipe (which is not ok), or just breath in from the pipe, and breath out elsewhere (you will need some valve that will regulate the flow here).
No, I think the issue is that your lungs can’t generate enough negative pressure to respirate effectively through 20m of pipe.
They're not underwater. It doesn't take much pressure just to move air through a tube.
I assumed they were going to put a fan on it because otherwise it would be hard to even get a breath in, even if there was a check valve for exhaling.