"Everybody fall back to the G-Tap. The Imperials are all over this place. Fall Back!"
Morgan Katarn — Gnome-speakernotesListen (file info)[src]

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.

Its upper end was located in a cavern which provided also protection from air attack, amidst temporary buildings and structures

Volcanic action warmed crustal rock formations, compiled with an upwelling of magma, and the natural decay of potassium, thorium, and uranium. Heated water, bumped to the surface, would bring isobutane to a boil which would be forced through power-generating turbines.

In 1 BBY, it was the site of their last stand against Jerec's forces.