Sump Pump Drain Fitting

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.

I've discovered the fitting I referred to was patented by Basement Systems in 1996, and apparently is part of their basement waterproofing "system". I'm awaiting a reply from them regarding my ability to purchase just the fitting. I thought I'd pass this on in case anyone was interested.