On 9/6/2015 8:44 PM, GMC wrote:
The U shaped pipe under my garage floor has frozen the last 2 winters in
the lengthy extreme cold spells.

How do you *know* it is a "U shaped pipe"? Do you have visual access to it?
Have you probed it with a snake, etc.? Or, has someone just told you
that it is U shaped and that it is under your garage floor?

I have been away for 10 weeks each of the last 2 winters.

Don't you LIKE the cold weather? :

The first winter my house watcher flushed toilets
and ran water once a week. This resulted in a mess inside the house from
backing up after a few weeks.

Why did it back up? Did the house-watcher not notice that the pipe
was blocked/frozen? Or, did this happen in his absence?

The second winter I decided to skip
having him run any water in the house to avoid a repeat situation. What
I did not realize was the furnace gave off condensation (about 3 gal per
24 hours) and goes through the waste water pipes under the garage floor
through the U shaped pipe and out towards the sewer. This amount of
water also froze over time. The 2 feet depth on each side of the U freeze

Again, how do you *know* this? I assume your garage floor is a concrete slab?

solid. I am not 100% sure but it may start in the section of pipe under
ground just outside the wall of the garage. It took 4 hours of umbels
time and 1 hour of time from a guy with a steam jenny (sp?) to thaw it
out.
I have no idea how to keep underground pipes from freezing. This is a

You could "shade"/insulate the pipe before burying it! I.e., put it in
a material that is less of a thermal conductor.

You could also wrap them with a heating element and deliberately keep them
warm.

You could ensure an adequate flow of "room temperature" water is flowing
through them to keep ice from forming.

townhouse built on a slab. I know of 2 other homes on the street with no
one home for an extended period of time during this cold period that did
not have any issues.

So, what's different between your property and theirs? Sun exposure?
Soil composition? Different construction techniques??

Any suggestions on a solution?

What is the diameter of the pipe in question? Is it a typical 4" drain?
Or, something that *feeds* the drain pipe?