A nozzle for a fan assembly includes an air inlet, a plurality of air outlets, and an annular casing having an annular inner wall defining a bore through which air from outside the nozzle is drawn by air emitted from the air outlets and an outer wall extending about the inner wall. Leach fields are constructed by excavating trenches, placing a first row of filter elements at the bottom of the trenches, installing a drain pipe on top of the row of filter elements, placing a second row of filter elements on top of the first row and the drain pipe, overlapping the pieces of filter cloth to provide a barrier to the surrounding soil, and backfilling the trench with soil. At least one of the honeycomb units has a cross section perpendicular to a longitudinal direction thereof, the cross section having an area greater than or equal to about 5 cm2 and less than or equal to about 50 cm2.