fig8 comprises a plate 320 which extends radially of the wand 294 and of the length axes of the barrel 13 and the pump unit 100 the peripheral shape of the plate 320 conforms to the cross sectional shape of the front end of the barrel 13 so that the perimeter of the plate 320 is substantially flush with the outer periphery of the open front end of the barrel 13 and so that the plate 320 effectively covers the open front end of the barrel 13 the peripheral shape of the plate 320 and cross sectional shape of the front end of the barrel 13 in one embodiment is generally d shaped with a generally flat underside and a convexly curved top and sides the plate 320 is not intended to seal the open front end of the barrel 13 and so need not tightly abut same since the peripheral wall 297 of the cup 295 fits easily within the open front end of the barrel 13 the plate 320 extends radially outwardly beyond the cup 295 as seen in fig8 a and 8b the front cover 293 includes an annular flange 322 extending axially rearwardly therefrom radially snugly into the cup 295 of the coupling 292 to bottom rearwardly and sealingly against a resilient gasket 321 which is disposed against the front face of the base wall 296 of the cup 295 respective holes in the gasket 321 loosely surround the front nipple 302 and leave fully open the communication between the interior of the suction nipple 306 and the interior of the cup 295 the front cover 293 further includes a further annular flange 323 extending fixedly and forwardly from the plate 320 in coaxial alignment.