A draining system (5, 6) for a hydrocarbon storage tank, comprising: a recirculation duct adapted for the circulation of a fluid material, and also adapted to introduce a first end and a second end thereof into the hydrocarbon storage tank; a pump coupled to the recirculation duct and adapted to recirculate the fluid material in the recirculation duct so that sucks in the fluid material in a first part of the recirculation duct and pushes the fluid material in a second part of the recirculation duct; a drainage duct adapted for the circulation of the fluid material, and also adapted to drain the fluid material through one end thereof; a motorized drain valve coupled to the drainage duct and adapted to allow and prevent drainage of the fluid material; at least one probe (25, 26) for detecting the presence of water in hydrocarbon; and a unit configured to receive measurements of the at least one probe (25, 26); wherein the unit is also configured to stop the pump and open the motorized drain valve to enable drainage when the received measurements of the at least one probe (25, 26) exceed an established threshold, the unit being configured to stop the pump first and open the motorized drain valve afterwards; wherein the drainage duct is connected to the first part of the recirculation duct, and it is upstream from the pump and downstream from the at least one probe (25, 26); wherein the recirculation duct and the drainage duct are arranged so as to drain the fluid material through the drainage duct by pressure of a column of the fluid material in the recirculation duct and the drainage duct; wherein the recirculation duct comprises: a first duct in the first part, the first duct comprising an end adapted for introduction into the tank; and a second duct in the second part, the second duct comprising an end adapted for introduction into the tank; and wherein the at least one probe (25, 26) comprises a first probe coupled to a part of the first duct, the part of the first duct being a part arranged horizontally. a recirculation duct adapted for the circulation of a fluid material, and also adapted to introduce a first end and a second end thereof into the hydrocarbon storage tank; a pump coupled to the recirculation duct and adapted to recirculate the fluid material in the recirculation duct so that sucks in the fluid material in a first part of the recirculation duct and pushes the fluid material in a second part of the recirculation duct; a drainage duct adapted for the circulation of the fluid material, and also adapted to drain the fluid material through one end thereof; a motorized drain valve coupled to the drainage duct and adapted to allow and prevent drainage of the fluid material; at least one probe (25, 26) for detecting the presence of water in hydrocarbon; and a unit configured to receive measurements of the at least one probe (25, 26); wherein the unit is also configured to stop the pump and open the motorized drain valve to enable drainage when the received measurements of the at least one probe (25, 26) exceed an established threshold, the unit being configured to stop the pump first and open the motorized drain valve afterwards; wherein the drainage duct is connected to the first part of the recirculation duct, and it is upstream from the pump and downstream from the at least one probe (25, 26); wherein the recirculation duct and the drainage duct are arranged so as to drain the fluid material through the drainage duct by pressure of a column of the fluid material in the recirculation duct and the drainage duct; wherein the recirculation duct comprises: a first duct in the first part, the first duct comprising an end adapted for introduction into the tank; and a second duct in the second part, the second duct comprising an end adapted for introduction into the tank; and a first duct in the first part, the first duct comprising an end adapted for introduction into the tank; and a second duct in the second part, the second duct comprising an end adapted for introduction into the tank; and wherein the at least one probe (25, 26) comprises a first probe coupled to a part of the first duct, the part of the first duct being a part arranged horizontally.