Lock for locking a dip tube of a storage tank, the lock comprising: - an end-piece comprising lower internal thread near a rear opening thereof, the lower internal thread being constructed to mate with external thread at an opening of the dip tube of the storage tank, wherein the end-piece has a front opening and the rear opening and defines a through passage, the end-piece comprising: ∘ a connector section configured to be connected to the dip tube, ∘ a seat for accommodating a removable lock member, ∘ at least one locking rim which forms a stop against an outward movement of a pivotable locking pin of a removable lock member, - the removable lock member configured to be placed in the end-piece and to be removed from the end-piece, the removable lock member comprising: ∘ a front section configured to rest in the seat, the front section comprising: ▪ a base part and ▪ a cover device, wherein the base part defines a recess and wherein the cover device is positioned in the recess, wherein the cover device is connected to the base part via one or more connecting members which extend from a rear side of the base part into the cover device, ∘ a protruding part which protrudes from a rear side of the front section and comprises a pin cavity, ∘ a cylinder cavity which accommodates a cylinder lock configured to receive a key, wherein the cylinder cavity is defined by the cover device, by the base part and by the protruding part, ∘ the pivotable locking pin being accommodated in the pin cavity and being connected to the cylinder lock, wherein the pivotable locking pin is pivotable between: ▪ a locked position in which the locking pin extends outwardly from the protruding part, and ▪ an open position in which the locking pin is retracted in the pin cavity. - an end-piece comprising lower internal thread near a rear opening thereof, the lower internal thread being constructed to mate with external thread at an opening of the dip tube of the storage tank, wherein the end-piece has a front opening and the rear opening and defines a through passage, the end-piece comprising: ∘ a connector section configured to be connected to the dip tube, ∘ a seat for accommodating a removable lock member, ∘ at least one locking rim which forms a stop against an outward movement of a pivotable locking pin of a removable lock member, ∘ a connector section configured to be connected to the dip tube, ∘ a seat for accommodating a removable lock member, ∘ at least one locking rim which forms a stop against an outward movement of a pivotable locking pin of a removable lock member, - the removable lock member configured to be placed in the end-piece and to be removed from the end-piece, the removable lock member comprising: ∘ a front section configured to rest in the seat, the front section comprising: ▪ a base part and ▪ a cover device, wherein the base part defines a recess and wherein the cover device is positioned in the recess, wherein the cover device is connected to the base part via one or more connecting members which extend from a rear side of the base part into the cover device, ∘ a protruding part which protrudes from a rear side of the front section and comprises a pin cavity, ∘ a cylinder cavity which accommodates a cylinder lock configured to receive a key, wherein the cylinder cavity is defined by the cover device, by the base part and by the protruding part, ∘ the pivotable locking pin being accommodated in the pin cavity and being connected to the cylinder lock, wherein the pivotable locking pin is pivotable between: ▪ a locked position in which the locking pin extends outwardly from the protruding part, and ▪ an open position in which the locking pin is retracted in the pin cavity. ∘ a front section configured to rest in the seat, the front section comprising: ▪ a base part and ▪ a cover device, wherein the base part defines a recess and wherein the cover device is positioned in the recess, wherein the cover device is connected to the base part via one or more connecting members which extend from a rear side of the base part into the cover device, ▪ a base part and ▪ a cover device, ∘ a protruding part which protrudes from a rear side of the front section and comprises a pin cavity, ∘ a cylinder cavity which accommodates a cylinder lock configured to receive a key, wherein the cylinder cavity is defined by the cover device, by the base part and by the protruding part, ∘ the pivotable locking pin being accommodated in the pin cavity and being connected to the cylinder lock, wherein the pivotable locking pin is pivotable between: ▪ a locked position in which the locking pin extends outwardly from the protruding part, and ▪ an open position in which the locking pin is retracted in the pin cavity. ▪ a locked position in which the locking pin extends outwardly from the protruding part, and ▪ an open position in which the locking pin is retracted in the pin cavity.