Plastic Trends STI™ Gasketed Sewer Fittings are now fortified against stress and breakage to a degree never before available in a PVC sewer fitting. The company strengthened the branch intersections of the Tees, Wyes and Sanitary Tees in the SDR 35 line of STI™ Gasketed Sewer Fittings. Wall thickness of the 4" branch is now 192% thicker than SDR 35 and 115% thicker than SDR 26. Wall thickness of the 6" branch is now 94% thicker than SDR 35 and 46% thicker than SDR 26. The gasket is set deep in the hub for greater protection from angular deflection. Socket depths are designed for increased pipe support. Plastic Trends.