What action should not be taken regarding the tap system?

The action of returning beer to the cask should not be taken because this practice can compromise the quality and safety of the beer. When beer is dispensed from a cask, it loses its carbonation as it exposes the remaining beer to oxygen and bacteria that can spoil it. Once beer has been served, it may also pick up contaminants from the tap line, atmosphere, or serving equipment, which makes putting it back into the cask risky. This can lead to off-flavors, spoilage, or even health concerns due to potential contamination.

In contrast, regular maintenance of the tap system is crucial for ensuring that beer is served properly and remains in good condition. Keeping the tap area clean helps prevent any contamination or bacteria from influencing the beer's integrity. Lastly, adjusting or maintaining the pressure controls is necessary for ensuring that the beer is dispensed at the right carbonation levels.