Finished the under floor plumbing today, yet another thing that took longer than it seems like it should have. The challenge here is just being absolutely 150% sure that everything is exactly where it needs to be because once we nail on the subfloor there’s no possibility of moving anything.
The way we tackled this was to temporarily screw the last subfloor panel in and put the shower stall and the toilet in place and take real measurements and work from there. A long drill bit aligns the hole in the subfloor with the hole in the trailer pan, then it’s drilling with a hole saw from either side.
Our general strategy is to drop the sink toilet and shower drains straight out the bottom of the trailer where they can be easily set up in a variety of configurations depending on where the house is parked. Doing things this way not only avoids the significant challenge of trying to build a proper drain tree inside of a tiny house floor, but also gives the option to separate gray water, or cap off the sewage pipe altogether and switch to a composting setup.
For the sink and the toilet things are pretty easy because each of those has its own integrated P-trap so a pipe straight down is all that’s needed. The glued P-trap under the shower was more challenging because not only was there literally only exactly enough vertical space in the 6 3/4 inch floor cavity (how are other people doing this in narrower floors??), but it also needed to be dead on the shower drain position and be braced there firmly enough for the tight push fit of the drain later. Making a template while the subfloor was still in place was helpful in finding that position later on!