A method of removing sand from a biological slurry tank, the slurry tank comprising access port at a bottom region of the tank for access from outside the tank to the bottom region, the access port comprising a valve for closing and opening the access port, the access port having a free inner diameter D1, which is the largest diameter of a circular cylindrical pipe fitting through the access port; the method comprising: - providing a pipe guide and attaching an end of the pipe guide to the access port by a liquid tight connection, the pipe guide having a cylindrical inner wall with an inner pipe guide diameter D2; - providing a pipe slidingly in the pipe guide with liquid-tight sealing between the pipe and the pipe guide to prevent leakage between the pipe and the pipe guide; the pipe further comprising a water conduit inside the pipe for transport of water through the pipe and a suction duct inside the pipe, separate from the water conduit, for transport of sand through the pipe to a suction unit; - moving a front end of the pipe through the access port into the bottom region of the tank by sliding the pipe inside and along the pipe guide; - pumping water through the water conduit to the inserted front end of the pipe for loosening sand in the bottom region of the slurry tank and removing the loosened sand from the bottom region by suction through the suction duct, wherein the pipe guide diameter D2 is smaller than the free inner diameter D1 of the access port for unhindered motion of the pipe through the access port, and the method comprises expelling water at the front end of the pipe around the suction area and by suction pumping the watered sand into the suction duct, characterised in that at the front end of the pipe, the suction duct is located centrally and the water conduit peripherally around the suction duct, wherein the pipe has a longitudinal axis, wherein the pipe is provided with a flow guide arranged and configured to angle the injected water relative to the longitudinal axis of the pipe. - providing a pipe guide and attaching an end of the pipe guide to the access port by a liquid tight connection, the pipe guide having a cylindrical inner wall with an inner pipe guide diameter D2; - providing a pipe slidingly in the pipe guide with liquid-tight sealing between the pipe and the pipe guide to prevent leakage between the pipe and the pipe guide; the pipe further comprising a water conduit inside the pipe for transport of water through the pipe and a suction duct inside the pipe, separate from the water conduit, for transport of sand through the pipe to a suction unit; - moving a front end of the pipe through the access port into the bottom region of the tank by sliding the pipe inside and along the pipe guide; - pumping water through the water conduit to the inserted front end of the pipe for loosening sand in the bottom region of the slurry tank and removing the loosened sand from the bottom region by suction through the suction duct, wherein the pipe guide diameter D2 is smaller than the free inner diameter D1 of the access port for unhindered motion of the pipe through the access port, and the method comprises expelling water at the front end of the pipe around the suction area and by suction pumping the watered sand into the suction duct, characterised in that at the front end of the pipe, the suction duct is located centrally and the water conduit peripherally around the suction duct, wherein the pipe has a longitudinal axis, wherein the pipe is provided with a flow guide arranged and configured to angle the injected water relative to the longitudinal axis of the pipe.