Sorry if this is a noob question, but I couldn't find it in the search.  How do I remove the gas tube?  I already took out the piston but can't figure out how to remove the actual tube.  Thanks in advance.

I will assume that the gas tube extends from the gas block all of the way to the gas tube nut in the upper receiver.
Remove the gas regulator by rotating it counter clock wise until it comes free from the gas block.
Once this is done, you should be able to see a small pin hole on the underside of the gas block where the gas tube screws in. There is a small pin in the hole that must be drifted out. Once this pin is removed, rotate the gas tube counter clock wise until it comes free of the gas block. Now, rotate the gas tube nut counter clock wise until it comes free of the upper receiver.

If you are one of the very young and have only seen digital clocks, counter clock wise means turning it to the left.

Exactly the info I was looking for, thanks for the quick response.