The hold unloading lines (41) are integrated into the lot unloading line (42) for each lot hold set (11).

Finally, the apparatus includes an outlet transfer line (90) from the discharge port of the pump for transfer of the liquid to a remote container (82).

The unloading tube may include an elevated portion (20) permitting passage of personnel and equipment when the unloading tube is in use.

The unloading tube is pivotally supported so that it can be swung out of the way when not in use.

The non-return valve is arranged to take its open position if the pressure prevailing in the volume (V1) exceeds the pressure prevailing in a discharge conduit connected to the outlet means (5).