How do you replace a PVC hose on a Mazda 6 2006?

This shouldn't take more than 15-20 minutes and you only need one tool:

Do this with the engine COLD, or you risk serious burns form the EGR assembly nearby! Grab a 10 mm standard socket (not deepwell). If that wont work, take a decent size pliers and carefully grab the square shoulders of the PVC and twist gently back and forth, then continue to turn counterclockwise 1/2 rotation. A squirt of wd40 before starting also helped loosen it. Loosen the driver's side bolt on the bracket that is on the firewall above the manifold. Attack it from the right and you will have ample clearance.

Slap an extension on there and remove the left bolt. Tuck the bracket out of the way to the right.

With some tongue and groove pliers, grab the snap ring on the PCV hose on the manifold. Squeeze it and rotate it back and forth until it loosens up, then slide it toward the firewall.

Grab the hose below the plastic elbow with your hand. Twist it back and forth while pulling up on it. It will come off pretty easily once it gets moving.

You will see the PCV valve. Grab a 15/16" deep well socket. Shove it down onto the old PCV valve until it engages the square flange. Twist it counterclockwise and the PCV valve will pop off (and should stick in the socket). Be careful not to let any crap fall into the valve cover (hopefully you washed it and let it dry first).

Shove the new PCV valve into the socket. Guide it down into the hole in the valve cover. Twist it clockwise until it fits snugly. You can remove the socket and examine your progress, if you wish, since it is easy to stick the socket back on there if it needs a bit more of a twist. But you shouldn't have to. (it's probably a 180 degree twist, maybe less.)

Reverse the remainder of the procedure for re installation

You're all done. Most Mazda modding gurus recommend changing the PVC every 5,000 mile oil change as this engine has problems using oil because of bad PVC design. The replacement valve is listed at AutoZone as "1001". Its only 6 dollars and could save your engine.