Whistle slot
Whatever you do you need a "Whistle Slot".
The whistle slot is a small razor blade slit in breather hose, along the first straight length of the hose, near the engine. The idea is the slit is its closed when the pressure is low. Its not a gaping open hole. However if there's a blockage down stream, the crank pressure has an alternate place to blow out. Consider it like an alternate air-door on your engine induction.
What happens if the breather is blocked with no way to vent? Well you can blow out the engines forward crank seal and blow massive amounts of oil all over the plane. The resulting loss of oil, loss of visibility thru the windscreen could be critical and has been in the past, so it's not a trivial installation.
Some guys use the clear thick vinyl tube from the aviation department at Home Depot or Lowe's. I think those might be subject to collapsing if bent too tight and don't recommend. The reason for the thicker rubber hose is not for the working pressure but to keep it from collapsing and getting kinked, like when you bend a drinking straw. You can use automotive rubber but test it that it keeps shape and can't be collapse easily by bending or squeezing. I used some hose and aluminum tubing. My alternate air path was a hole in the aluminum tubing with a rubber flap laying over the hole. Cheers George RV-7
