Our Sub-Zero(model 650) refer has

Question

Our Sub-Zero(model 650) refer has a a whiteish corrugated tube that comes down the back of the refrig. and hangs above the middle of the drain pan in the back. Every two weeks we have to remove the overflow of water that collects and freezes behind the crispers, and eventually ends up leaking onto my hardwood floor. We blow air down into the tube and a lot of brown gunk is deposited into the drip pan. How can we fix this?