Yes. In most homes, the shower, toilet, sink and tub all drain into the same line on the way to the main sewer. What matters is how they connect.
How it works
Each fixture drains through its own short pipe and trap, the curved section that holds water to block sewer gas. (A toilet's trap is built into the porcelain; a shower's is under the floor.) Those pipes then join a shared branch drain that carries everything to the main line.
The rules that make it work
- Pipe size. Plumbing codes set 3 inches as the minimum drain for a toilet. A shower drain is smaller, commonly 2 inches. The shared line has to be big enough for everything on it. See should a toilet drain be 3 or 4 inches?
- Venting. Drains need air to flow smoothly. Without it, water rushing down the toilet can suck the water out of the shower's trap, letting sewer gas into the bathroom. Codes allow some bathroom fixtures to share a vent (called wet venting), but only in specific layouts.
- Slope and fittings. The line has to fall at the right slope and join with the right fittings so waste moves in one direction.
Moving or adding fixtures usually needs a permit and inspection. See can I do my own plumbing in Arizona?
What gurgling tells you
If the toilet gurgles or bubbles when the shower drains (or the other way around), it usually means:
- A clog further down the shared line, so water is pushing air back up, or
- A venting problem: a blocked or missing vent, so the drain pulls air through the toilet instead.
If several fixtures are slow or gurgling at once, the problem may be the main line. See signs of a sewer line problem.
When to call
- Gurgling that doesn't stop.
- A sewer smell in the bathroom (a trap may be getting siphoned dry).
- Water backing up into the shower when you flush.
OX Plumbing handles drain cleaning, camera inspections and drain repairs, 24/7.