I have a furnace condensation drain that sometimes freezes...heater cable good idea??

[Anonymous]

...the drain goes from above garage, down the exterior side of house and out the side of the garage. When we get continuous days of below freezing temps it the pipe freezes. I am able to do quick fix of pulling the flexible furnace drain out and placing it in a bucket. Not a big deal as we luckily don't get weeks and weeks of below freezing temps. But I thought there has to be a better way of keeping the drain from freezing. I was looking into a pipe heater cable but all of them seem to only work if wrapped around the exterior of the pipe. As my pipe is behind drywall - except for short piece sticking out from exterior wall - I was looking to see if there was any sort of heater cable that goes INSIDE the PVC pipe???