The Geothermal Tap, or G-Tap for short, was a geothermal energy spring on Sulon, secretly built by Rebels to provide for their independence from both the Galactic Empire and the SoroSuub Corporation.
The principle of the G-Tap was built on a simple technology that existed since the time of the Galactic Republic, allowing for water, heat and energy without dangerous radioactive technologies, and governmental taxes. The colonists had to sell their shares and drill the shaft themselves to that end.
Its upper end was located in a cavern which provided both protection from air attack, and was close to the natural heat source; the interior had a main chamber, caves, vaults, and a passageway that led to the "back door", a flat area above. Around the cavern the colonists nearly completed a complex of temporary structures that housed turbines, injection pumps and their controls.
Volcanic action warmed crustal rock formations, compiled with an upwelling of magma, and the natural decay of potassium, thorium, and uranium. Had the project been completed, the colonists would pump the heated water to the surface, bring to a boil which would be forced through power-generating turbines. A canyon intended to become a river that would feed the G-Tap led to the cavern.
In 1 BBY, Imperial forces attacked Sulon and many Rebels thought it was targeted against the G-Tap, and they moved to defend it. It was the site of their against Jerec's forces; and the defenders retreated into the cavern before overwhelmed by the ever-advancing Imperial commandoes.