My filter was in the cabinet that GalsofEscape mentions.
I never installed the filter, but I did leave the filter housing in place in the event a subsequent owner might want to use the filter.
We are on our own well with excellent water. We boondock exclusively, so I only drink our well water. Thus no filter.
1. There should be a filter housing wrench to help remove the clear plastic housing.
2. As HondaMan174 said, bring plenty of towels, because the filter lives either just above all the electrical stuff...or in the space with the electrical stuff.
3. If you drain your water system, you can be sure that the only water you must deal with when removing the filter housing is the water in that housing. The outside shower is very close, and you can use it as a "low point drain" along with the low point drains at the curb-side rear of the rig. Open your faucet and shower inside to help the water drain out.
4. I had to replace my pump, and it quickly became obvious from the rat's nest of wires in that space that the easiest way to handle things was to actually remove the converter/fuse/breaker panel from the front of the cabinet. I didn't disconnect anything. I just removed the screws and slid it out to give me room to work and a better chance of keeping things dry. When done, I just slid it back into place, installed the 4 screws, installed the front cover, and it was done.
Before you button up, fill and pressurize the water system and check for leaks. Nothing ever leaked in my rig, but you certainly don't want leaks around all that electrical gear.
You'll soon discover that the shelves, etc. in the rig are made out of tissue paper, and they are attached to tissue paper. The small 3/4" x 3/4" cleats upon which the shelf sits are attached with wood screws to 1/8" thick paneling. It's a joke. While you're in there, do yourself a favor. Mount all the cleats on the paneling using Gorilla Glue. Screws will act as "clamps" while the glue dries. Then use screws to attach the shelf to the cleats. In my rig, the cleats kind of fell off into my hand when I removed the shelf .
Be careful where you drive screws. There's a LOT of wiring in that space. The factory actually drove a screw right into 14/2 120 volt wire in that space...and they just backed out the screw and left the damaged wire!!
While you're in there, strengthen this shelf. Use the glue to make a proper joint between the cleat and the wall paneling, because screws simply don't hold in 1/8" paneling...but the glue does wonders. One warning. Gorilla Glue acts a bit like Great Stuff foam insulation...it expands and makes a mess. In this application, that's not an issue. In others, adjust accordingly.
Other applications. When a screw falls out...as they will now and again...especially if you boondock...use a slightly larger screw and Gorilla Glue to put it back. It will never fall out again. I keep a well-stocked kit of stainless steel screws, bolts, nuts, etc for these repairs. Stainless won't rust and it's compatible with aluminum. The difference in cost for small quantities is insignificant. Over the years in my HW-277, I had to replace screws holding the table base, microwave, all manner of cabinetry, appliance rails outside, and, and, and.... Upsize slightly and add Gorilla Glue. One and done.
If you need black screws, you can buy them, but not in stainless. It's easier to have all stainless in the right sizes, and paint the ones you need to be black. Screw them into cardboard, use Rustoleum to spray the screw head, let it dry 24 hours (so it won't get banged up when you screw it in). If you get some Gorilla Glue ooze, spray a bit of paint in a paper cup and use a disposable artist brush to touch up. Easy peasy.
While I'm blustering, if you have the outdoor kitchen, the sink drain flexes a lot, and it may eventually crack. As it turns out, you can repair it with new hose...or better, you can get the thin-wall plastic drain plumbing for a bathroom sink and use a short piece as a sleeve inside the flex pipe and hold it with a couple of hose clamps. https://www.acehardware.com/departme...E&gclsrc=aw.ds
It helps to use sandpaper to taper the end of the pipe a bit and add a little lubricant (e.g. dish soap) to help ease the pipe into the hose. I used the same technique when my fresh-tank fill hose developed a leak where a screw through the floor (holding a cabinet) chaffed the hose and made a hole. I trimmed the screw point with a dremel tool, then patched the pipe with a sleeve cut from drain pipe. Worked better than new.
More on plumbing: If you have the outdoor kitchen, the inside kitchen drain plumbing must Tee into the outside kitchen drain plumbing and then head off to the grey tank. Once again, if you boondock over rough terrain, that Tee may crack. Since this is all ridged plastic plumbing, that presents a real problem. Answer: Fernco fittings. https://www.lowes.com/pd/Fernco-1-1-...E&gclsrc=aw.ds
You'll have to cobble in a coupling or two with some straight pipe, but the Fernco Tee allows you to "insert" the Tee in place in that rigid pipe!! Not only that, but since the Tee cracked from stresses in the first place, this flexible rubber Tee solves the stress problem.
If you boondock...you will soon discover that your stairs are VERY vulnerable. You can see how tortured mine are. They hang down in harm's way. I used to carry a 6# sledge to straighten them out so they were usable once on site...then again at home. So I quickly bit the bullet and added a lift kit to the torsion axle...you can see it at the far end of the axle in the pic. That adds about 3 1/2" of lift to the rig. You'll probably need to get a different ball mount so the rig rides level down the road. AND you'll need a GOOD step ladder so you can deploy and secure your awning. And stowing the bed ends requires a bit of extra gymnastics. I am 6'6" tall, yet I used one of these to help push in the canvas. https://www.acehardware.com/departme...E&gclsrc=aw.ds
Soft and sturdy...with a long reach. I had a 3-step ladder and it was BARELY enough even though I'm tall. 4 steps minimum. But to be able to go essentially anywhere my 4WD pickup can go, it was worth it. And let's face it, the roof on a HW is way up there even if it's not lifted. You need a really good ladder.
What's that other contraption under my rig, you ask? That supports the freshwater tank. After years of boondocking, mine gave up the ghost. I replaced the tank and used this super-easy to make and install support to keep it from failing again. The picture explains the "design". That's just 1/2" galvanized water pipe...more than strong enough for the job. And it fit in the "looms" already installed on the underside of the frame with no mods.
If you're going to boondock, ask me about solar. I had solar on mine, and I could camp essentially indefinitely. I can help with how to install panels on the roof...a whole other story. See pic of my solar mounted on the roof.
Much more than you asked for, but if you're new to this rig, there's a lot that can be helpful.
P.S. Be sure to treat your canvas...especially the seams. You're about to enter the 10th year for this rig, and a little TLC can keep the canvas from falling apart. And this tape can be very helpful for small punctures and tears so long as they are NOT on the seams. https://www.etrailer.com/Accessories...xoCGsgQAvD_BwE
Take your time, round the corners, have something solid behind the canvas (and a helper to hold it), and rub it down thoroughly. Works great. There are other brands, too.