PURPOSE: To facilitate maintenance of a nozzle assembly by rotatably providing an annular collar having openings for jet of cleaning solution outside a tubular stem one end of which is closed and which has openings for jet of cleaning solution around its peripheral wall and disposing the openings of the collar in the direction opposite to its rotation in such a way that the collar is rotated by the force of jet cleaning solution from the stem through the openings of the collar.

CONSTITUTION: A nozzle assembly to be disposed in a drain tank comprises a tubular stem 20 whose upper end 20a is open and is coupled to a cleaning solution supply source and whose lower end 20b is closed and a rotatable annular collar 40. The tubular stem 20 has a midsection 32 with a reduced radius and a plurality of openings 35 spaced apart around it. The collar 40 includes a plurality of openings 64 disposed thereabout which extend reversely of the direction of rotation. With such a construction, cleaning solution from openings 36 of the stem 20 is jet through the openings 64 of the collar 40 into the drain tank. At that time, since the direction of the openings 64 is opposite to rotation, the collar 40 rotates in reaction and disperses the cleaning solution.