Bathroom plumbing covers everything from swapping a leaking faucet to running the full rough-in for a new bath. The work that matters most is the part that gets covered up. Drain lines need proper fall so waste carries. Vents need to be sized and placed so water can move without pulling traps dry. Connections have to be right the first time, because getting back to them means removing finished tile.

The trap and vent relationship is the piece most people have never heard of and the one that causes the most complaints later. Every fixture has a trap holding a little water that blocks sewer gas from coming up the drain. When a fixture drains, moving water wants to siphon that trap empty, and the vent is what lets air in behind it so the seal stays. Undersized or badly placed venting is why some bathrooms gurgle, drain slowly, and smell.

So on a remodel we care about where fixtures are moving to and what that does to the drain slope and the venting, before anybody picks a vanity. On a repair we care about why the thing failed. Either way we would rather explain what is happening behind the wall than hand you a number and start cutting.

Toilets fail at the floor. The wax ring seals the toilet to the flange, and it compresses once. Any rocking movement breaks that seal, and then every flush pushes a small amount of water under the toilet instead of down the drain. That water goes into the subfloor for months before anything visible appears, so by the time the tile looks wrong there is often damage underneath it.

Showers and tubs fail at the pan and at the connections. Water that gets past a failed pan liner or an unsealed joint at the valve travels along the framing and shows up somewhere else entirely. In a slab house that can mean a wet spot several feet away, which is why a leak in a bath often needs proper locating before anyone starts pulling tile.

Remodels create their own problems when fixtures move. Relocating a toilet or shower means new drain routing, and drain lines need consistent fall. Not enough and waste sits in the line. Too much and water outruns the solids and leaves them behind. Add the venting requirements and it becomes clear why a moved fixture is real plumbing work and not just extending a pipe a few feet.