Because of the possibility of reservoir siphoning, all systems that have any portion of the nozzle circuit lower than the top of the reservoir will need an anti-siphoning valve. In the event of tubing rupture, the valve will allow air to enter the line and stop the possibility of siphoning the reservoir. The nozzle circuit between the anti-siphoning valve and the rupture may still siphon, but the contents of the reservoir will be protected from this effect. The anti-siphoning device requires two parts: a union tee and an anti-siphoning valve. Place the union tee directly in the tubing as it comes out of the pump. This union tee will be used prior to any other fittings, including nozzles, in the line. Insert the anti-siphoning valve into the top of the union tee. Mount the valve in a vertical position. (MistAway only supplies one sided anti-siphoning valves to protect from installing the valve in the wrong position.) The valve must be installed with the arrow, direction of flow, facing the union tee. To begin the nozzle circuit installation, insert the tubing into the remaining opening in the union tee. (MistAway recommends purchasing the anti-siphoning valve from us, as it must have a cracking pressure not to exceed 1.5 PSI. and come complete with viton seals.) The anti-siphoning valve will not need to be used if the entire nozzle circuit is installed at an elevation higher than the reservoir top. The anti-siphoning valve is necessary only in drum based systems. The 2006 Gen II model will not require an anti-siphoning device in any situation.