to include an up flow inclined plate separator of a style well known in the filtration art see e g u s pat no 4 120 796 and the prior art patents therein cited in an inclined plate separator incoming water is directed to the bottom of the tank where it enters and flows upwardly through spaces between a series of spaced apart and upwardly inclined imperforate plates particulates flowing between the plates tend to agglomerate and fall by gravity to the bottom of the tank where they can be removed through a lower drain line as already described an overflow collector can also be positioned at the upper end of the inclined plate assembly to collect suspended oil or grease which can then be decanted from the upper end of the tank use of the optional inclined plate separator is recommended where incoming water from the washing installation is unusually dirty or contaminated with large amounts of oily residues second pump system 42 and booster pump 64 are actuated only when a vehicle is passing through the installation to be washed in a more fully automated system the pressure gauges described above may be replaced by conventional pressure transducers and associated electronics to provide an audible alarm signal when filter differential pressure rises to a point showing the need for filter cleaning manipulation of complex valve systems as required for backwashing filters in conventional filtration systems is completely eliminated in the system of this invention all mesh filters in the system which require periodic cleaning are readily accessible from the surface and can be quickly removed and cleaned when the pumping systems are not in operation a particular feature of the invention is the use of only unrecycled.