GeoSiphon systems (patent pending) induce contaminated groundwater flow through permeable treatment media by utilizing a siphon between two points of hydraulic head difference. A siphon is a closed conduit that conveys liquid from a point of higher hydraulic head to one of lower head after raising it to a higher intermediate elevation, at sub-atmospheric conditions (negative gauge pressures or vacuum), without external power input. All surface waters and groundwaters contain dissolved gasses, which degas within a siphon due to the vacuum and temperature within the siphon. Bubbles form, and if not properly managed will accumulate in the siphon, gradually reducing the flow rate until the system is ultimately shut down. Therefore appropriate management of gas within a siphon is the primary factor that must be considered to maintain continuous siphon flow. This report provides an overview of GeoSiphon technology and generic details concerning de-gassing in siphons and associated gas management methods.