fitting 34 having an outlet end 36 lying near the top of the sludge trap 24 in the form of a barrel 38 the fitting 34 passes through an opening 40 in the top 42 of the barrel 38 which is air and liquid tight another air and liquid tight passage 44 is provided for the outlet fitting 46 which is connected to a hose 48 leading to the optional filter 26 very importantly the fitting 46 includes a vacuum relief passage 50 which preferably is set at 4 20 psi preferably 10 15 psi the optional filter 26 contains a pair of small fittings 52 54 the outlet fitting 54 of which is connected to a hose 56 which in turn is connected to a positive displacement pump 58 the pump outlet 60 passes to a return hose 62 which then has an outlet 64 in the customer sump 22 the positive displacement pump typically operates at about up to 5 15 psi and draws fluid from the sump 22 including bottom sediment and other sludge like constituents and causes them to pass through the hose 32 to the inlet fitting from here the sludge falls to the bottom of the trap 38 while the liquid phase enters the fitting 34 under the influence of the vacuum created by the pump 58 as long as the pump can pull a partial vacuum liquid flows through the lines 48 56 while liquid and sludge pass through line 32 the sludge falls out and.