I notice in this house I got recently that there's a leak in a drain
pipe in the garage. At the least, I know the washer is connected to it,
and I can see a little water leak out right at the slab after the washer
has drained. I've been able to get the same leakage after pouring about
3 gallons of water down that drain. The leak isn't an emergency, but
the carpet in the room touching the garage is getting moist.

I don't think the water is coming from higher up. There is a T-junction
where the washer drain meets this vertical pipe. I guess the seals
failed after time and they are now duct-taped together. Having wrapped
that in turn with paper towels and taping together, I caught no moisture
whatsover. A paper towl taped around the pipe just an inch above the
ground is also dry.

This leak wasn't caught in the inspection since the inspector didn't
test this drain. The inspector also happened to miss a ground wire
following the plywood on the roof, but lets not start ranting about that
now. This pipe goes through the slab and I presume it meets up with the
rest of the drainage someplace, somewhere. It must be leaking at or
near where this pipe first touches the slab.

What are my options? Is this exclusively the domain of plumbers? I
fear I'll have to get somebody to break down the concreate around this
pipe so they can do anything. The only fix I can think of right now is
sealing that pipe to the concreate using Plumber's Goop, but that too
will likely fail quickly. Any ideas?