Basement toilet bubbles from air

1940’s house, 1 floor, toilet on first floor, install new toilet in basement,
cut into floor and cast iron waste pipe, y connected to main pipe. Main stack is original up to roof. When the toilet on main floor is flushed the toilet in the basement actually bubbles from air backup. Both toilets flush ok to remove waste. What is the problem and how do you fix.


Sounds like a venting issue to me. It’s sucking wanted air from the basement area due to its proximity (being closer than the main vent). Too many bathrooms on one vent?

The main vent pipe might have to be upgraded to a larger pipe.

My exact first thought.

The new toilet is too low.

Fix: add a pump out.

Is it pushing air out or sucking air in??

A vent problem will typically cause it to suck air due to siphoning. If it’s blowing bubbles it could be partially obstructed sewer line or a low spot / trap in the sewer line which would allow air pressure to build up when the higher toilet is flushed. A partial obstruction in the line could cause it to either blow or siphon or even blow then siphon.

Try filling a tub and letting the water go. See if that causes a reaction as the tub empties (be prepared to stop it if it backs up through the toilet). If water rises in the toilet, the sewer line is probably obstructed.

Cover the toilet with Saran wrap. If it expands, it’s blowing air, if it pulls in, it’s sucking air. I don’t know what to do with the information, but it sounds like a cool experiment!:shock:

Lot’s of good ideas as to what the problem is, but I know how to fix it. Call a plumber.

Whatever is most cost effective…

That sounds like a college dorm prank.:smile: