A support and connection structure suitable to support a tank during a hydrostatic acceptance test and suitable to connect the tank to a feed line of a test fluid, said structure comprising: - a support and housing base for the tank; - a sealing joint with an axial extension along an axis and a circumferential extension perpendicularly to said axis, configured to connect the support and housing base with the tank, a feeding conduit axially passing through the fluidic connection between the feed line and the inside of the tank being obtained in said sealing joint, wherein the support and housing base comprises a clamp formed by at least one pair of jaws (40a, 40b) configured to pass from a disengaged position to a support position of the sealing joint along said circumferential extension and of the tank along said axis, a joint housing seat and a connecting pipe for the connection of the feed line with the feeding conduit also being obtained in the support and housing base, wherein the sealing joint comprises a base engagement element sealingly engageable with the support and housing base, and a connecting nipple, the connecting nipple extending between a first end engageable in the nipple engagement hole, and a second end (52") at least partially externally threaded so it is engageable in a respective threaded hole obtained in the tank, the structure characterized in that the base engagement element comprising a centering portion and a head which surmounts said centering portion in axial succession, wherein i) the centering portion is engageable in the joint housing seat with shape and/or force coupling, ii) the head has a greater circumferential volume than the one of the centering portion, a nipple engagement hole configured to engage the connecting nipple also being obtained in the head. - a support and housing base for the tank; - a sealing joint with an axial extension along an axis and a circumferential extension perpendicularly to said axis, configured to connect the support and housing base with the tank, a feeding conduit axially passing through the fluidic connection between the feed line and the inside of the tank being obtained in said sealing joint, wherein the support and housing base comprises a clamp formed by at least one pair of jaws (40a, 40b) configured to pass from a disengaged position to a support position of the sealing joint along said circumferential extension and of the tank along said axis, a joint housing seat and a connecting pipe for the connection of the feed line with the feeding conduit also being obtained in the support and housing base, wherein the sealing joint comprises a base engagement element sealingly engageable with the support and housing base, and a connecting nipple, the connecting nipple extending between a first end engageable in the nipple engagement hole, and a second end (52") at least partially externally threaded so it is engageable in a respective threaded hole obtained in the tank, the structure characterized in that the base engagement element comprising a centering portion and a head which surmounts said centering portion in axial succession, wherein i) the centering portion is engageable in the joint housing seat with shape and/or force coupling, ii) the head has a greater circumferential volume than the one of the centering portion, a nipple engagement hole configured to engage the connecting nipple also being obtained in the head. i) the centering portion is engageable in the joint housing seat with shape and/or force coupling, ii) the head has a greater circumferential volume than the one of the centering portion, a nipple engagement hole configured to engage the connecting nipple also being obtained in the head.