Pentair 21" and 25" Sand Drain plug

The Pentair Sta-Rite 21" and 25" System 3 Sand Drain Plug (part number 24900-0503 or 24900-0503Z) is a specialized structural maintenance fitting engineered exclusively for the lower containment chassis of Pentair Sta-Rite System 3 filtration networks. This heavy-duty, 1-1/2 inch plug is cross-compatible across the entire System 3 platform, securing the drain ports of the SS Series high-rate sand filters (models S7S50 and S8S70), the SD/SMD Series Diatomaceous Earth (D.E.) filters (models S7D75 and S8D110), and the SM Series modular media cartridge systems (models S7M120, S7M400, S8M150, and S8M500).

Injection-molded from a dense, high-impact, and chemically inert polymer composite, this plug's primary operational role is twofold: it provides an absolute watertight and airtight compression boundary during normal operations, yet serves as a dual-purpose sand and water removal access point during service intervals. When threaded down tightly against the bottom tank fitting, it allows the high-capacity, pressurized vessel to safely handle massive fluid volumes and sustain continuous internal system operating pressures up to 50 PSI without weeping, material deformation, or backing out under heavy pump vibration surges.

During seasonal winterization cycles or extensive filter changeouts, the plug can be removed to cleanly evacuate stagnant water or flush heavy media deposits, preventing structural freeze-cracking of the fiberglass outer shell. Engineered to withstand a lifetime of outdoor equipment pad weathering, shifting thermal stress, and direct UV exposure, it completely resists degradation from concentrated pool sanitizers like chlorine, bromine, and winterizing acid flushes. Due to its wide-diameter, thick-walled threaded profile, this individual sand drain plug carries a net product and shipping weight of approximately 0.30 pounds.