Once I’d finished the water delivery pipes, I got right into the drainage system for the Tiny House and it went a lot easier and more quickly than I had expected.

I’d previously planned a drainage system on paper and bought a bunch of 1.5″ ABS and various connectors and P-traps that I thought I’d need. Funnily enough when I bought the sheep wool insulation from Oregon Shepherd, I also purchased the white mesh that you saw me pinning up in those videos (not published yet sorry). Anyway, they rolled that white mesh up onto a 4′ length of 1.5″ ABS, so I was able to use that in my plumbing system; AWESOME!

After a little careful planning of holes through the floor and googling the required drop / slope of the piping, I set to it.

Planning the drainage Route

The trickiest part was navigating around the heater exhaust pipe and the axles.

Not knowing how much the axles will travel upwards, I wanted to keep the piping above the lowest part of the trailer framing, that way the pipes will be out of harms way. Thankfully this was fairly simple; running from the kitchen sink in the middle of the axles, out past the rear axle where I used two 45 degree elbows to drop the pipe a little so that it can receive the piping from the bathroom sink drain.

I dry fitted it all together first without glueing it, just to make sure it all worked out.

After the bathroom sink joined the main line, I stepped the size up to a 2″ pipe using a T-joint that has two 1.5″ ins and one 2″ out. This then ran out towards the shower at the rear where I thankfully, due to the height of my trailer, had enough room to install a 2″ P-Trap under the shower.

After connecting this up, I needed to step it up to a 3″ pipe, simply so that I may connect an RV style pipe connector. This, seen below, allows me to connect a flexible RV sewage hose.

An adaptor can be bought from an RV shop ready to receive the flexible sewage hose


All plumbing systems need venting, with most homes having a vent stack exiting through the roof. Due to the fact that I only have an 8′ length of plumbing receiving only three drains, kitchen sink, bathroom sink and shower I opted for an air admittance valve in the kitchen. This allows the pressure to equalise when draining water, but keeps the gasses in the system. This valve has to be placed above the highest P-trap in the system.

The composting toilet will have it’s own separate vent stack.

Fixing it all into place

Once the route had been planned and all the various lengths of pipe trimmed down to the right lengths, it was time to glue them all together.

One thing I learned through my research is that you must not put too much slope on your drainage. Here’s why:

The P-traps in a drainage system are designed to hold water so that sewer gasses can not come back up the pipe and into the home. If the sewer pipes are too steep then the water gets sucked out way too fast, causing a vacuum effect that can pull all the water out of the P-trap too; leaving a clear run for the noxious gasses to enter your Tiny House.

I also didn’t want the pipes to run too close to the ground, making sure I had optimum clearance from the ground. It all worked out pretty well and I had the whole thing installed in less than 5 hours.

For additional support, I simply attached some small cedar blocks to the plywood underside of the trailer and used a coated and galvanised strapping to hold the pipes in the right place. I was surprised how solid the system is once you’ve added the glue. Take great care when using the ABS glue, it can make your head spin if you don’t use a mask. And it pretty much locks in immediately, so make your connections quick and accurate.


Finishing it off inside

As we have chosen a composting toilet, we do not have to plumb in the toilet, which makes life a little easier. This would however need a different system, as you are not meant to plumb toilets into the same pipes as your grey water.

I have not yet terminated the pipes inside as I am waiting until the sinks are in place so that I can make sure things are lined up as best they can be. Stay tuned for that update.

As I write this, I have already started to install the propane lines and things are going well. It will almost be time to test out the water heater!