On May 24, 9:11 pm, DerbyDad03 wrote:
My basement toilet has started to erupt as a bubble of air blows water
up and out. As far as we can tell it happens on a random basis. We'll
lift the lid and the underside will be all wet. My daughter was
walking through the basement and heard - well, she heard whatever
sound a large under water bubble would make.

Let me describe the drain and vent set-up:

First: This toilet has been installed for as long as I have lived in
the house (25+ years) and has never bubbled before. Nothing has
changed as far as the venting or drains. The toilet flushes fine and
all other fixtures drain normally.

Second: This bathroom is in the corner of the house where all the
drains meet under the slab just before leaving the house. The toilet,
shower and sink in this bathroom are the last set of fixtures before
the drains leave the house. The toilet is before the shower and sink
which wye into the main sewer pipe about 3 feet from the exterior
wall. There is a clean-out just inside the exterior wall under the
sink.

Third: My house has only one vent - the soil stack, which is in the
opposite corner from the bathroom. No fixture in the house has it's
own vent, and never has. Right or wrong, this has never been an issue.
All fixtures have always drained properly.

So, based on the information above, can someone explain why my toilet
has suddenly started erupting like Mount St. Helens?

Thanks!

I'm not a plumber or expert, but the one thing that stuck in my mind
is that this apparently "just" started happening and is on a "random
basis." To me, that would rule out a fixed obstruction, or something
that has grown into place over time.

Does the event happen when multiple people might be flushing/rinsing/
showering at the same time, or can you recreate the issue with a
single event (a flush, shower, dish wash, etc.)?

Do you hear gurgling or other noises from other toilets, sinks, etc.?