Where a container is to be abandoned underground, as much liquid LP-gas as possible shall be _________ through the container liquid withdrawal connection.

When abandoning a container underground, it is crucial to ensure that as much liquid LP-gas as possible is removed from the container through the liquid withdrawal connection. This practice is essential for safety reasons, as leaving liquid LP-gas in an abandoned container poses risks of leaks, pressure build-up, and potential hazards associated with gas accumulation in the surrounding area.

Removing liquid from the container minimizes the risk of explosion or fire, as well as environmental contamination. In contrast, the other options do not address the safety concerns appropriately; storing or refilling the tank is not advisable at this stage, and venting alone does not ensure the removal of the liquid content. Overall, the correct action to take is to remove the liquid LP-gas to comply with safety procedures and regulations when abandoning a propane container underground.