Quality GFS Wastewater Tank: What Defines a Reliable Bolted Tank A quality GFS wastewater tank is defined less by its price than by the evidence behind it: a documented ISO 28765 calculation, a verified enamel, and a complete inspection file. The Glass-Fused-to-Steel (GFS) coating must survive pH swings and abrasives for decades. Engineered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel), these bolted tanks are built so the quality is provable, not claimed.