The drain service of Pure Mechanical GroupMetro Vancouver + Fraser Valley
Drain problems · Noises

Toilet bubbles when the shower runs

Water going down one drain should never move the water in another. When the toilet bubbles or its level rises and falls while the shower runs, the pipe they share is restricted and the air has nowhere else to go.

Andrew HendersonReviewed by Andrew Henderson, Red Seal plumber and founder of Pure Mechanical Group. Last reviewed November 2026.

Drawing of a horizontal drain line under a floor with a blockage being cleared
The toilet and the shower share a drain under the floor

What it usually means

A partial blockage in the shared branchOnly that bathroom is affected. Hair, soap and paper where the shower and toilet lines meet.
The main sewer lineThe lowest toilet in the house bubbles, and it happens when the washer or an upstairs tub drains too. A backup is on its way.
A blocked ventThe toilet bubbles and flushes weakly, and nothing is actually slow. The vent through the roof is blocked.
A full septic tankOn septic, bubbling at the lowest toilet is a classic sign the tank needs pumping.

What to check yourself

  1. Work out which toilet does it. If it is the lowest one in the house, think main line.
  2. Run the shower for two minutes and watch the bowl. Rising water is more serious than a few bubbles.
  3. Run the washing machine through a drain cycle and watch the same toilet.
  4. Check the other bathroom. If it behaves normally, the problem is in the first bathroom's branch.
  5. If the water in the bowl rises, stop using water and call. It is about to come out somewhere.

Stop and call a plumber if

  • The water level in the bowl rises
  • Water appears in the tub or shower when the toilet flushes
  • It is the basement toilet
  • There is a sewage smell

Call 1-800-604-0631, any hour.

What fixing it costs

If it is the bathroom's own branch, it is cleared through the toilet or a cleanout for a flat clog price, from $269. If it is the main line, from $649. We find out which before we start and tell you. Those are regular-hours prices (9 to 5, Monday to Friday). Outside those hours every price is double. Each covers up to 2 hours on site, and the drain is tested in front of you before we leave.

A blocked vent is hourly work: $289 for the first hour on site and $189 an hour after.

Questions people ask

Is it urgent?

Bubbles alone can wait for regular hours. A rising bowl, or water appearing in the tub, cannot.

Could it be the toilet itself?

No. A toilet cannot make itself bubble when another fixture is used. The cause is in the pipe they share.

Will a plunger fix it?

It may shift a blockage that is right at the toilet. If the bubbling comes back within a day, the restriction is further down.

Rather have a plumber look?

Call 1-800-604-0631Book a plumber