Tiny House Plumbing

Tiny house plumbing...seemingly so easy but fraught with difficulty. I designed my plumbing system to be minimal with the kitchen sink placed adjacent to the shower so the interior wall between could be my plumbing wall. I purchased a Bosch Tronic 8 gallon electric water heater and placed it beneath the sink in a stainless steel pan made of leftover material from my shower pan. Water heaters can either have their pressure relief valves directed into pans or out through the floor or wall of a building. Since I wanted to minimize exterior penetrations, I decided to direct mine to a pan.
I used 12" flexible 3/4" copper hoses to connect the water heater to the brass fittings reducing to the 1/2" PEX system. The cold water in comes through the floor (see photo below) via a frost free hose bib connected to a water hose and outdoor spigot. The water is directed into the water heater which, when connected to electricity, will heat the water and send it out the hot side to the sink via the braided flex line and shower via PEX tubing and brass elbows. The cold follows a similar path. In the shower, the mixer valve combines hot and cold in varied amounts depending on handle rotation. I used clamp rings to secure the tubing to the elbows and in line connections. It requires a special tool that I borrowed as well as a tubing cutter. (You can buy the push fittings but I was told by some plumbers that they are not as great for long term durability.) The clamp tool requires significant strength to tighten the rings but when it is dialed in, you only have to squeeze to the point when the tool releases. If it's not tight enough, the tool stays connected to the ring. Fairly straightforward. Make sure you leave 1/8"-1/4" of tubing end visible between clamp and fitting to ensure a good connection.
The tubing is somewhat flexible but cannot really make 90 degree turns quickly so I used elbows in those junctions. There are also T fittings which can help direct water to other fixtures but I didn't need them in this situation. I used red tubing for hot and blue for cold which is not really necessary (you could do all of one color or even all white) but I like color coding things so that was kind of fun. Just make sure you check the labels on the fixtures if you color code so they match up with the PEX colors and hot/cold indicators on the escutcheon plate.
I used a drop ear 90 up top to screw in my shower head which I will be directing toward the back corner of the space. I added blocking behind both the drop ear 90 and mixer valve in order to mount them. The front face of the mixer valve needs to be flush with the finished wall surface so you have to know what thickness that's going to be before adding the blocking. I actually swapped out the 2x4 blocking for the mixer valve for a piece that is only 1" thick since I decided to go with a 3/8" marine grade plywood coated with epoxy paint for the walls (see the next blog post about that).
Once I ran the supply lines, I started working on the drain system. For the sink, I used an S trap so I could drain out the floor. A P trap can also be used to drain out the wall. I needed an extension tube to continue the vertical piece through the floor since my system is taller than typical.
I added an ABS adapter under the trailer to connect the drain to a short piece of 1 1/2" tube and then to a rubber coupling which transitioned the size from 1 1/2" to 2" to match the diameter of the shower drain. I used ABS cement to attach a piece of 2" tubing to an elbow, let it dry, slid it into the coupling and tightened the metal ring with a screwdriver. From there, I added a length of 2" tubing to the shower drain.
I added an exterior p trap to the shower drain again connected by a rubber coupling attached by metal clamps secured with screws. These couplings will enable me to easily disconnect the drain system when I want to move my house. 
I added a vent to the system which allows air in so the water can flow out easier and faster. Ideally you have one of these for each fixture but since my system is so small and a short run, I was told I really didn't need any venting. Since the area under my sink is open and I wanted to use chrome fittings, I couldn't find a way to make a vent there look good. I will see how well the system works and if I feel like it needs to be changed, I can explore those options in the future.
When we did the first test on the system, there were so many leaks! First in the outside spigot to hose connection (a different fitting and a clamp solved that problem), then in the connection between the hose and frost free hose bib (just needed to be tightened), then in the brass connections between water heater and PEX/braided sink connects. I tried to tighten those connections which was difficult to do in place then retested but still found leaks. I asked a friend to help me take everything apart and use new Teflon tape tools to get those joints water tight. Also part of that process was replacing the flexible copper hoses since they had developed pin leaks from too much bending and one actually broke off while I was trying to disconnect it, shooting water out onto the floor until I could tip it upright. Hopefully that didn't do too much damage after I got the water mopped up and a fan running. Once we re-installed everything, all of the supply joints looked water tight. All of the PEX joints looked good from the start so I was thankful for that. The sink strainer was leaking so I took it apart, cleaned things up, applied new plumbers putty, re-installed and it seems good to go after another water test. The sink faucet is still leaking a little at the base which is somewhat worrisome since I had all of the internal components replaced when I had the new copper tubes braised on. Not sure what's going on there but it's an old faucet so maybe nothing can be done. Worst case, I have to remove the sink to take out the faucet, find a new faucet, have new holes drilled in the sink and re-install. Read the post about my farm sink for more details about that component. Now I can start focusing on my electrical system so I can not only have running water, but hot running water!

Check out my flickr for more photos!