a unitary reservoir in fig . 1 made of plastic , preferably made by blow molding , comprises a plurality of hollow bulbs , and with centers along a curved line in a plane , at least one bulb being a mounting bulb having a mounting tower or extending from said bulb , said mounting tower comprising a solid portion enabling mounting of the reservoir and a hollow portion that communicates with the interior of said mounting bulb and acting to resist bending of the solid portion .