Keith Nuttle wrote in
:

On 12/21/2014 2:10 PM, Larry Blanchard wrote:
I put a seal over the drain and filled the shower basin with water
up
to the 3-4" ledge. It took better than 24 hours to gradually leak
under the seal, which was just one of those flat rubber disks. So no
leak in the shower stall floor.

I would recheck the drain. From your test you have no idea of what
leaked around the seal, and what leaked into the basement.

I would agree with this. Depending on how the drain is made,
there may be a very short tube going into a rubber sleeve
which fits over the drain pipe - those can fail to seal
sometimes. Otherwise, like Mike said, I'd suspect a cracked
pipe - note that PVC does not like to bend, and will eventually
crack if it's been forced to bend around a joist or something.

Then someone on this group mentioned the air vent on the sink itself,
or as everyone things it is the overflow.

It did not take long to clean the blockage in the over-flow/air-vent
and the sink has worked perfectly since cleaning it out.

For some reason ants love to build a nest in there, in my
house. They come in thru the window and set up housekeeping.
When the sink stops draining I know to get the ant spray
first, then clean it out.

John