A method of assembling multiple hydrocyclones, wherein the multiple hydrocyclones have a base end and an apex end, at least an inlet chamber for fluid to be cleaned positioned at the base end, at least an overflow chamber for an overflow portion of the fluid, a separation chamber having an elongated shape between the base end and the apex end and at least an underflow outlet at the apex end, characterized in that the overflow chamber is positioned at the apex end, the inlet chamber having at least two side openings positioned on opposite sides of the inlet chamber, the hydrocyclones being arranged at a support structure for support of the hydrocyclones, the hydrocyclones being arranged side by side with their side openings adjacent each other thus forming an inlet pipe by means of the inlet chambers, the inlet chambers forming the inlet pipe being adapted to be pressed against each other, wherein the hydrocyclones are arranged on a support structure at one of a base end and a head portion and are pressed together.