Do NOT use teflon tape there. Teflon tape will prevent the head from securing all the way down and thereby using it would not to allow the o-ring to seal completely. Water is passed through the resin bed in the opposite direction of normal flow, which flushes suspended matter out of the resin tank. Water Softening resin beads are not water soluable and have a negative electrical charge. The sodium ions attach to the resin beads.
Untreated water enters the resin tank and passes through the bed of resin.
The calcium and magnesium ions attach to the resin beads and the sodium ions are released. The resin beads exchange the sodium ions for the hard water ions allowing soft water to flow from the resin tank. Since the resin beads prefer the calcium and magnesium ions, the slow rinse allows an overwhelming concentration of sodium ions to overpower and force the calcium and magnesium ions off of the resin beads and are then discharged down the drain. During this cycle, the brine tank is being refilled with more water to create the brine solution for the next regeneration.