Both the grey city water knob inside and the small spigot drain are threaded, so normal tools (wrench or pipe wrench) will work for either... uh, come to think of it, that's assuming that the PO didn't modify it to be threaded.
Winvest. You are correct that the tool to remove and install the little crimp rings on our water lines are fairly expensive. After my second bone-head, user-error, absent minded forgetting to drain the water lines in below zero temp water burst, I broke down and bought the tools. I think I got it on eBay.
However, it has proven invaluable. SMB was willing to send me the tool and have me mail it back to them but I figured I would be stupid again so I just broke down and bought it. I needed 10 inches of water line but Lowe's only sold it in 50 foot increments or something.
So, if anyone on the board needs a few inches (or a few feet) or waterline don't hesitate to drop me an email and I can cut a length and mail it to you. Its just sitting in storage right now. It's blue (cold water) color if that matters.
I think its called a PEX (or Zurn) Crimp tool. I want to say mine was about $100 and its suitable for a variety of size tubing and included a couple of crimp rings, etc. You can get the tubing, crimp rings, elbows, T's, etc at Lowe's, they just don't sell the actual tool. I bought the version that comes in its own little storage box and includes the de-crimping tool also (which is a necessity). I opened the package, read the instructions and practiced on a few crimp rings and climbed under the van and got the job done pretty quickly and easily.
The one thing that I would recommend is also buying a tubing cutter (some packages come with it). They basically look like a pair of anvil garden shears with a little razor blade guillotine. It is really important to cut the tubing squarely so that the crimps and the tubing all line up nicely and these do the trick. I saw a pair for sale at harbor freight for like $4. They're cheap and worth the investment.
I don't actually carry the thing around in the van since I'm usually not out for that long and I have enough duct tape and hose clamps to limp along. But it is a nice little thing to have.