It’s All Downhill From Here (Plumbing)- Kitchen Sink and On-Demand Water Heater

Renovating our 1997 Fleetwood Mallard for Full-Time Living (Part 25)

This is the story of how my husband and I purchased a 20-year-old travel trailer and I DIYed the crap out of it to make it suitable for full-time living. In this series, I’m giving All of the details about the process step-by-step, as performed by me, a 26-year-old woman with No experience in construction. The first installment in this series is called “The Wind Rose: The Beginning”, detailing the purchasing process and the changes I planned to make. You can find that article in the link below and start at the beginning. Then, follow along in the series by clicking on the link for the next article at the bottom of each page.

Kitchen Sink

As you have hopefully read in the previous posts, the original kitchen in our 1997 trailer was absolutely unacceptable to me. I subsequently decided to completely rebuild it with a lot more counter space. The principal plumbing problem of the rebuild was moving the sink. The original placement was in the front left corner of the trailer, directly next to the stove. I decided to move it to the front wall of the trailer directly under the front window.

All of the plumbing for the sink ran along the wall of the trailer inside the cabinets. The sink drain was black ABS that sloped gently down to the grey water tank drain near the shower. The cold water was flexible PEX that connected to the hot water tank, the potable water inlet behind the couch, and the freshwater tank under the couch. The hot water line came directly from the hot water tank. As I’ve mentioned in my other plumbing posts, the trailer plumbing is pretty straightforward and uncomplicated. The most difficult part was getting the plumbing to interface with the new hot water heater.

I cut all of the old lines just below the elbows and left the stubs on the floor for the duration of the renovation. In the picture below you can see the outline of the new kitchen on the floor and the partially-built new shelves. The black ABS pipe is visible behind the frame for the over and the white PEX water lines are on the floor up against the far wall. The copper LPG line is also visible coming up to where the over will be reinstalled. There is a black hole in the wall of the trailer where the old hot water tank was. I decided to install the new on-demand water heater in the same place and I discuss that in detail in the second half of this article. The new sink will be just around the corner from where the old sink was. It was pretty simple to extend the existing pipes to reach the new space with an elbow in the corner to keep them running along the wall.

Once I had more of the shelving built and knew the exact location of the sink I was able to start working on the kitchen plumbing. I left a space in the shelving for the water heater and began to extend my pipes. The black ABS is standard and the same drain pipe you will find in houses, which makes it cheap and easy to find. Similarly, the 1.5 in water lines were cheap even color-coded for hot/cold water. The original water lines were both clear, but I like the color-coding to keep the two lines straight during the installation.

I installed a new length of ABS pipe with a connection fitting to make it reach the corner and then installed a 90-degree elbow in the pipe to turn to the corner. Then I added another length of the pipe until it was long enough to reach the center of the new sink location. The biggest concern with drains is to keep a clear downward path without any sagging low points where water might collect. We want everything to flow nicely down the pipe and into the grey water tank without slowing down. Interestingly, I also discovered that having a pipe be Too Steep is also a possible issue, as the water can leave food scraps or fats behind on the pipe if it moves too fast. There is an ideal slope for drain pipes; 1/4in down per foot traveled. Now you know. My pipe was going to meet that requirement handily in order to go over the hot water heater. It was simple and quickly done, although I didn’t glue everything in until I was Absolutely sure it was correct. Gluing is permanent, so I left that until after the sink and water heater were installed and I was sure it was correct.

Darin pipe and new water lines going around the corner from where the old sink was.

Connecting the sink itself had to wait until the countertops were installed. However, after that it was simple. Purchasing a regular sink, such as you’d have in a house, allowed me to use regular plumbing methods as well. The sink drain that came with the sink I purchased had a threaded end that fits nicely into the HepVo 90-degree adaptor. If you haven’t heard me raving about the HepVo waterless valve, then go back and read the other plumbing articles. These things are the best and I honestly don’t know why they aren’t using them in regular houses as well (probably something about “the code”). They save room and eliminate many of the problems with p-traps and u-bends that occur in RVs and trailers.

Kitchen Sink Plumbing: Sink drain → HepVo 90-degree adaptor → HepVo → 1–1/2" female threaded adaptor → 90-degree street elbow → run of pipes to the grey water tank.

The sink drain connection to the HepVo and then the drain pipe.

The hot and cold water lines were a bit more complicated because of the hot water heater. The cold water PEX tubing comes from the fresh water tank under the couch, goes behind the fridge, and travels along the wall to the hot water heater. From the water heater, it splits and also goes forward to the kitchen sink. The hot water comes out from the water heater and goes in both directions, forward to the sink and backward to the shower/bathroom sink. It was a simple matter to extend the PEX tubing to the location of the water heater, add a 3-way connector (see more about this below), and then extend it around the corner to directly under the sink. These pipes will along the wall under the kitchen counters and be out of sight and out of the way of the shelving. From the floor under the sink, I simply extended the lines up the back wall to the kitchen faucet. All of these pipes are hidden behind the shelving and under the countertop, so that gave me a lot of room to work with and improvise. Make sure to dry-fit everything before you start clamping and gluing. Get it all set up and double-check everything before you permanently fix it into place.

The PEX lines and drain pipe extending around the corner behind the shelving.

The new plumbing for the kitchen was pretty simple and runs neatly along the walls behind the kitchen cabinets/shelving. The final puzzle was installing the on-demand water heater to replace the 6-gal water tank.

Plumbing dry-fitted with uninstalled sink before countertops were put in.

On-Demand Water Heater

When I bought the trailer I knew that the original 6-gal water heater was a no-go. As far as water heaters go, 6 gallons is pretty small and really isn't enough for a full-timer. It’s enough for a really, Really quick shower or a small load of dishes and never at the same time. I’m not planning on rationing my hot water every day for the next few years, so I decided to rip out the old and put in a new, on-demand, tankless water heater.

The old water heater tank and connections for the old sink.

I decided early on that I wanted an on-demand (tankless) water heater for many reasons. An on-demand water heater is more energy-efficient than a tank heater because it’s only on while you’re running the water and only heats exactly as much as you need. Water tanks keep the water in the tank hot at all times, ready to be used. That means the propane is constantly kicking on and off to keep it at a good temperature. I didn't want to waste propane heating water that I wasn't using, and the on-demand water heaters are the answer to that. Amazingly, trailers and RVs have almost entirely switched over to tankless water heaters in recent years and they make models specifically for trailers that are a 1:1 fit with the old water tanks. That means you can simply pull out your old water tank and put a new tankless heater in the same hole as an exact fit. Perfect!

After doing the research and finding our exact fit model we fit it into the hole in the trailer and the space I left for it in the shelving. The water heater has one connection for cold water and one connection for hot water, which makes it pretty simple. It also requires a DC electrical connection to run, so make sure to run some wire into the corner. Remember to leave room for the LP gas pipe as well, which connects somewhat awkwardly on the side. It was tricky getting that LP pipe into place without kinking the copper and having to replace it, which is Not a job for amateurs.

I cut my hot and cold PEX lines above the water heater and added a 3-way connector. That allowed me to extend a leg of the water lines down to the water heater connections, so water would travel all 3 directions. Cold water would come from the water tank and go into the water heater and to the cold water faucet at the same time. Hot water would come out of the water heater and run forward to the sink and/or back to the shower and bathroom vanity at the same time. It was annoying getting all the fitting and elbows and connection in place, but not hard to figure out. I decided to install some stops in the line after the water heater just in case we needed to cut the water off to Only the kitchen sink and not the shower or vanity, say if we were installing a new sink or fixing a leak. I also installed stops at the other end of the water line near the shower and vanity, in case we needed to shut the water off to the back of the trailer and not the kitchen. I didn’t want the black drain pipe to touch the water heater, just in case leaking heat would damage it, so I pinned it up at the corner.

Hot and cold water PEX connecting to the new tankless water heater.

The one problem we had with our water heater involved the new LPG regulator that we installed on our propane tanks. The regulator is a necessary part of propane safety and you really need one. We bought a new one to make sure it was safe and working and followed the recommendation for our trailer. However, our trailer was recommending a pressure regulator that was the right size to manage propane for the oven, the fridge, and the 6-gallon water heater. The pressure regulator was Not the right size for our new tankless water heater, which required a higher flow of propane than the other appliances. So for 6 weeks, we lived in a trailer with no hot water while we tried to figure out what was wrong with the water heater. We rewired the electrical, we checked the LP lines, we ordered a new one to replace it in case there was a manufacturing problem. Finally, we called a repair service and they diagnosed the problem over the phone and ordered us a new regulator with a larger capacity. Once we screwed on the new regulator, our on-demand water heater Immediately started working. What a relief! Lesson learned. Friends, make sure to buy an LP pressure regulator that is sufficient for your on-demand water heater.

The plumbing and water heater barely visible in the overall scheme of the new kitchen.

After over a year of using the on-demand water heater, we are very happy with it. The water heater comes with a control panel to adjust the water temperature and we set it at 115 degrees and haven’t changed it. We had a bit of trouble with low water pressure in our RV park. If the water pressure flowing through the water heater is too low, the heat won’t kick on as a safety measure. Usually, that means we have to run the cold water for 10 seconds to get it going full blast before switching it over to hot to make the heater kick on. It’s also difficult to mix cold and hot without the low pressure causing the hot water to turn off, we set our temperature at a comfortable showering temp and don’t mix cold water in. Our propane use has been Very low, we only have to refill our propane tanks every other month! I don’t know how much of that is the mild temperatures on the Oregon Coast, our electric space heater, or the water heater, but I appreciate the low cost all the same.

Our finished kitchen in use!

Overall, I’m so pleased with the new kitchen and the plumbing, although it’s invisible, is a necessary foundation for everything the kitchen does. We haven’t had any problems with clogging or water not flowing. So far, so good, one year later!

Writing to you from beautiful Coastal Oregon (Tillamook area), I’m a Forest Service Botany Field scientist, backpacker, farm wife, DIYer, and writer.