How do my 1996 Roadtrek water lines connect?

[VTPete]

Ok, this may sound like a crazy question. Forgive me!

I just dropped and serviced my fresh water tank. I thought I would also replace the water filter, which now uses an easy to access bottom filter.

But, I won't be able to twist it onto the existing grey-colored water line tubing. If I twist it onto the water line, it will untwist from the tank.

So, my question is with regards to those grey colored water lines and how they connect. I can't tell by looking at them if they are twist on compression fittings, or if they are pvc lines all measured cut, twisted and then glued in place. I don't want to put a wrench on them and try to untwist them if the are glued.

Here's a photo for you. Maybe they make a connector like the one on the end that has a reverse thread on one side to pull the two pieces you want to connect together?
-Pete