There is a special PVC fitting that connects to the 1-1/2" sump pump discharge pipe on the outside of the house. The fitting transitions from 1-1/2" to 4" PVC, but the unique thing about it is there are slots at the top to provide an air gap and to allow water to exit should there be a clog in the drain line. I've seen this fitting on several houses, but am unable to find one locally, or on the Web. Any help would be greatly appreciated. Thank you.