I installed the plumbing for a private use bathroom, which is a fancy way of saying a normal residential bathroom that still has to follow real plumbing rules.
The job came down to three systems. Water supply, drainage, and venting. All three have to work together, because plumbing is cruel and one tiny mistake can ruin your day.
I started with the rough in. That meant placing the pipes before the sink, toilet, and shower went in. I had to make sure the drains lined up, the water lines landed in the right spots, and nothing was wildly crooked. Easier said than done when you are staring into a wall wondering if you understand anything.
For the drainage, I set the pipes with the right slope so waste could actually leave. I aimed for about 1/4 inch of drop per foot. Too flat, and things sit there. Too steep, and water runs ahead like it has somewhere better to be. The sink also needed a trap to block sewer gas, because apparently civilization depends on a bend in a pipe.
The venting mattered too. Vents let air into the system so the drains do not gurgle, siphon the traps, or act possessed. I made sure each fixture had a proper way to breathe.
Then I ran the hot and cold water lines. The sink needed both, and the shower needed a mixing valve so nobody gets boiled alive because someone flushed a toilet nearby. Small detail. Pretty important.
I also secured the pipes so they would not sag, rattle, or make weird noises in the walls. Plumbing already causes enough emotional damage without adding mystery sounds.
Before closing anything up, I checked for leaks and tested the fixtures. I had to make sure water comes in, waste goes out, nothing leaks, and nobody smells sewer gas.