I have a similar setup with my sump pump here in Illinois. PVC pipe going out the house, then a long flexible plastic pipe to take the water away from the house. What I did was drill a lot of small holes in the flexible pipe that lies in the lawn with a drill and bit. This allows the hose to act as a sprinkler and distribute the water more evenly. When the sump pump is done the remaining water can drain out the bottom of the hose through the holes, so no water is left trapped in the hose. It also acts as air vents in the hose, so the water can drain without suction (or else the hose can stay filled with water towards the house, if no air can get in). I have had no freezing problems with this setup.