When you are setting up a water system into your basement bathroom, you will already need 2 major things in place: a main vent shaft or sump pump draining system to get your waste water into the main sewer line, and a source for your clean water feed. These 2 components will allow the bathroom to take in water and remove waste without causing issues. In basement systems, you will need to have the main drain below the level of the bathroom itself, as waste moves downward from gravity—or if your drain is above your basement, you will need a sump system to pump the water up and into the main sewer vent.
Step 1 - Connect Main Waste Lines to the Drain
At the base of the drain, your sink should have a trap in place to keep fumes from moving back through the drain and up through the sink into the air. This drain line then runs into the main vent shaft so that the waste can move out of your basement with ease. Your main water feeds should come in through from your main water supply to the bathroom, where you can run the water feeds to your since faucets.
Step 2 - Install the Pressure Fittings
To get fresh water into your basement bathroom, you will need to tap into your existing water lines. Turn the main water feed valve into the Off position, and then use another sink in the home to drain the line.
Once this is done, you can then cut into your main water lines and attach a split T pressure fitting. This will attach to your main water line and provide a pressure fitting on one end for your nylon water feed that will run to your sinks and toilet. Use the plumbers tape on all threads before attaching lines to the faucets and on main water feeds of your toilet to prevent high pressure water leakages.
Step 3 - Install Shower Lines
It will take more work to install lines if you did not plan the shower's water lines when you started the project. You will have to run the main lines into the shower wall in your basement bathroom using copper fittings and splits to get your piping to the faucet's intake. You will run a main line to the base of your faucet controls and then up to the shower output as well. Again, be sure to use plumbers tape on all threaded ends of your lines to prevent leakage.
Step 4 - Shore Up the Lines and Check for Proper Drainage
Once your nylon feed lines are attached from hot and cold, under your sink faucets and the cold feed to your toilet, you will want to check all your water lines in your basement bathroom to ensure they run properly and drain without issue.