How to remove custom nav bar back button - swift

Question

I am adding some subview to main view controller. When I add one of these subview, I create a custom back button so that it will go back to main view controller, not the prior view controller in the navigation stack. I can add it programmatically but I can't seem to figure out how to delete it. Any help is greatly appreciated!
func createCustomBackButton() {
self.navigationItem.hidesBackButton = true
let customFont = UIFont.systemFontOfSize(26.0)
UIBarButtonItem.appearance().setTitleTextAttributes([NSFontAttributeName: customFont], forState: UIControlState.Normal)
// customBackButton is a property I set for UIBarButtonItem
customBackButton = UIBarButtonItem(title: "<", style: .Plain, target: self, action: "back:")
self.navigationItem.leftBarButtonItem = customBackButton
}
func back(sender: UIBarButtonItem) {
UIView.animateWithDuration(0.3, animations: {
self.containerView.alpha = 0
}, completion: { finished in
self.view.sendSubviewToBack(self.containerView)
self.navigationItem.hidesBackButton = false
// what do I do on this line to get this to disappear or set to nil??
self.customBackButton = UIBarButtonItem(title: "", style: UIBarButtonItemStyle.z, target: self, action: nil)
// clears out prior view that was there to free up memory
for view in self.containerView.subviews {
view.removeFromSuperview()
}
})
}

Answer 1

Using self.navigationItem.leftBarButtonItem = nil will reset the leftBarButtonItem back to the default.

Answer 2

You should use an unwind segue. If you're using storyboards, drag from the "destination viewcontroller" to the thing that looks like a sideways share button (exit button) of the VC you want unwind from. Name it whatever you'd like, we'll call it "unwind"
and then call in the same VC:
self.performSegueWithIdentifier("unwind", sender: self)
in the VC you want to unwind back to:
#IBAction func unwindToMapSegue(segue: UIStoryboardSegue) {
// do something
}