Question:

What are the most common mistakes in installing a toilet?

Common plumbing mistakes

Putting in a toilet is a complicated business, with plenty of opportunity for error. One way to avoid mistakes is to call a plumber. However, if you insist on operating without a license, this list should help you avoid some of the most common amateur mistakes.

1. Scoffing the law, that is ignoring and/or violating local code restrictions.
2. Using pipes that are too small. Toilet requires its own 2" minimum vent and at least a 3" diameter drain.
3. Fitting copper to galvanized. Unless you put a brass or dielectric fitting between the two, you'll get corrosion, and eventually, a failed union.
4. Not using Teflon tape or pipe compound at threaded joints. These sealants fill in the imperfections in the pipe threads to provide a more leakproof seal.
5. Not leveling your fixtures at installation. You need to use a level to level the bowl. You may have to stick in a few shims under the bowl. While you're at it, make sure the toilet is lined up square to the wall.
6. Not installing an air gap filling for fixtures. This may seem like a minor point, but unless you provide a gap between potable water and a drain, waste water could back up into your drinking water. Not a good thing.
7. Chopping your supply stub outs too short, so when you put on your finished wall, you don't have enough tube sticking out to install shutoff valves. Measure twice, cut once.
8. Improper alignment of tubes into stop valves or fittings. Make sure that the compression ring (“olive”) is set straight before you start tightening on the nut.
9. Failing to flush debris from your water lines when turning the water in the house back on. Always run the outside hose valve or flush your toilets first. This will get rid of any air or dirt in the lines.