Why Does My Toilet Bubble When the Bathtub Drains?

Bubbles in a toilet bowl

When your plumbing system works the way it should, it’s easy to forget all about it. But when a problem catches your attention, the plumbing becomes all you can think about until you resolve the issue.

Perhaps you’re experiencing a toilet bubbling when your shower drains. Learn more about what can cause this problem and how to fix it.

What Causes Toilet Bubbles When the Tub Drains?

The toilet bubbling phenomenon stems from something called wet venting. Plumbing codes require all drains to be vented separately to prevent pressure buildup and to vent sewer gases outside. However, when several fixtures are so close together in the bathroom, a single vent pipe may facilitate multiple drains, including the tub, sink, and toilet.

When a drain or vent blockage occurs in this type of configuration, air may enter and exit through one fixture when you use another. This is what makes the toilet bubble or sink gargle when the bathtub drains. You may also notice that all the bathroom fixtures are slow to drain and the toilet flushes sluggishly when a blockage forms in a wet vented system.

How to Troubleshoot Air Bubbles in the Toilet Bowl

The clog causing air bubbles in the toilet may be minor or quite severe. To help you determine how serious the problem is, follow these troubleshooting tips.

Clear the shower drain

Remove the strainer and clean any hair and soap scum from it. Then, insert a plumbing snake into the drain. This removes obstructions a foot or two down.

Plug the tub and fill it with a few inches of water. Release the plug, and as the water drains, keep an eye on the toilet. If the bubbling persists, you know the blockage is further down.

Clean further down the drain

One option is to pour drain cleaning chemicals down the shower drain, but we don’t recommend this because repeated use of chemical cleaners can deteriorate your plumbing. Plus, do you really want to send all those chemicals into the drinking water supply?

It’s better to use safe enzyme-based cleaners, baking soda, peroxide, or salt. You can also use a longer plumbing auger to reach further into the plumbing system.

Of course, if the toilet is bubbling, it’s also affected, which means; plunging the toilet; could be useful for clearing the blockage.

Clear the vent

If your effort to clear the plumbing doesn’t work, the blockage could be located in the vent. The main vent stack should exit through the roof. Pay a visit there, and you may discover leaves or other debris blocking the vent.

Remove surface debris and spray water down the vent to help clear obstructions further down. If the vent overflows, use a plumbing auger to remove stubborn clogs. Once cleared, consider installing a protective screen over the plumbing vent to prevent a repeat occurrence.

Why Call a Professional to Fix the Situation?

If these troubleshooting tips seem overwhelming, or you try them to no avail, call Mr. Rooter® Plumbing for help. Our experienced plumbers have the right tools and knowledge to fix the problem without causing further damage. We can also locate inherent problems with your plumbing, such as an uphill drain, that may be the root cause of air bubbles in the toilet bowl.