fig1 and 2 illustrate one form that the invention can take . the illustrated apparatus includes a storage tank catwalk assembly removably disposed in a cement pit structure . the pit structure consists of a bottom wall 10 , two side walls 12 and 14 , and two ends walls 16 and 18 . the two side walls are contemplated to be a predetermined width depending upon the width of the vehicle to be serviced ( usually approximately 3 feet wide ), whereas the two end walls are widely spaced , e . g . on the order of eighteen feet apart or as required . the defined pit is an elongated rectangular pit structure oriented to underlie a vehicle after the vehicle has been driven to a predetermined location on the floor 20 of the service facility . two of the vehicle wheels are shown at 22 in fig1 . fig2 is a broken away view of the storage tank walkway assembly , showing end areas of the assembly ; intermediate sections of the assembly are omitted so that structural details are scaled up to be visible . an oil storage tank 24 is shown resting on the pit bottom wall 10 . the tank includes a sheet metal bottom wall 26 , side walls 28 and 30 , end walls 31 and 32 , and a top wall 34 . certain ones of the walls may be flanged to facilitate welding operations at the seams ( joints ) where the various walls meet . the oil storage tank 24 further includes two parallel longitudinal skid bars , shown as channels 36 and 38 . the channels are spot welded to the bottom wall 26 at various points therealong to provide longitudinal reinforcements . as best illustrated in fig2 end portions of the skid bars may extend beyond the tank end walls 31 and 32 ; the exposed end of the bars 36 and 38 may be connected to cables or other lift devices used to lower the oil storage tank 24 into the pit structure or to lift the tank out of the pit structure . in the alternative , lugs 37 may be spot welded to both sides of the oil storage tank 24 at conveniently spaced locations such that a chain lift ( not shown ) may be used to lift the tank from the pit structure . in such embodiment the channels 36 and 38 would not extend beyond the tank end walls 31 and 32 . the oil storage tank 24 is designed to provide a storage reservoir for dirty oil taken from the serviced vehicles . the weight of the stored oil imposes an outward load on the tank walls . the walls may be reinforced against outward bulging forces by longitudinal tie bars 39 , 40 , 41 and 42 ; these bars extend the full length of the associated walls 26 , 28 , 30 , 32 and 34 and the number of longitudinal tie bars required is determined by the size of the tank as well as the load of the stored oil imposed on the side walls and bottom . spot welding may be used to connect the bars to the tank walls . tie bars 44 extend transversely between the bars 40 and 41 to constrain the side walls 28 and 30 against outward bulging motions . the drawings shows one bar 44 ; however , any number of such bars may be used at spaced points along the length of the reinforcement longitudinal tie bars 40 and 41 . additional tie bars 46 can be extended transversely between the longitudinal tie bars 39 and 42 . the ends of the additional tie bars are welded to respective longitudinal tie bars 39 , 40 , 41 and 42 or to the tank side walls as required . the tank bottom wall 26 may be reinforced against transverse downward bulge deformation by means of transversely extending reinforcement bars 47 ; any number of such bars , spaced along the length of the tank , may be used . the various reinforcement mechanisms are intended to maintain the tank structure configuration against deformation or leakage while enabling relatively thin gage sheet metal to be used for the various tank walls , thereby minimizing overall weight and material costs . overlying the oil storage tank 24 is a sectionalized catwalk structure 49 . in the embodiment of fig3 and 4 , support rails 50 and 52 are welded to upper side areas of the tank to form connection points for the catwalk structure . sectionalization of the catwalk into a reasonable number of sections , e . g . six sections , reduces the weight of each catwalk section , permitting the individual sections to be removed from the support rails 50 and 52 when it is desired to paint or clean the catwalk sections , or when it becomes necessary to remove debris from the area alongside the oil storage tank 24 . each catwalk section extends the full width dimension of the pit structure , i . e ., across the space between the pit side walls 12 and 14 . assuming a total catwalk length of sixteen feet and six catwalk sections , each section would have a length dimension of approximately 22 / 3 feet . each catwalk section is preferably formed of a plywood material , as shown for example in fig5 . a foraminous material may also be contemplated to enable oil , sludge or other debris to gravitate through the openings in the catwalk upper surface . any oil spillage will be absorbed by the plywood while any type of foraminous surface would also satisfy this objective . the aim is to keep the catwalk surface reasonably clean and slip - free . the fastener mechanisms for connecting the catwalk sections to the support rails 50 and 52 as shown in fig3 and 4 may be varied as to detail . as shown in fig3 and 4 , a representative fastener mechanism includes a bolt or screw 54 extending through a washer 56 into mesh with a nut 58 welded onto the undersurface of the support rail 52 . four such bolt / nut assemblies may be used to detachably fasten each catwalk section to the support rails 50 and 52 , two fasteners for each rail . the plywood material shown in fig5 may be secured thereto using any conveniently available glue intended for such purpose . it will be seen from fig1 and 4 that edge areas of the catwalk are relatively close to the pit side walls 12 and 14 ; the catwalk is substantially coextensive with the pit width dimension such that the mechanic is not likely to have his foot catch in any crack or joint at the pit side wall surface . the end edge areas of the catwalk sections are in near adjacency to one another , as shown at 49a in fig2 whereby the catwalk sections collectively define an unobstructed continuous walk - on surface along the length dimension of the pit . the catwalk sections will rather closely conform to the pit side wall spacing ; however , the catwalk assembly should not prevent initial installation of the oil storage tank 24 into the pit if the catwalk sections are mounted to the tank after the tank is in its installed position . it will be seen from fig2 that the tank end wall 32 is spaced some distance away from the pit end wall 16 , e . g . on the order of two feet . this space provides a clearance 60 at one end of the tank structure that facilitates human access to drain opening or pipe 62 extending from the tank end wall 32 . the drain opening 62 is not visible in fig2 but is shown in phantom in fig1 . a motor operated pump , not shown may be connected to the drain opening 62 when it is desired to pump oil and / or sludge out of the tank without lifting the tank out of the pit . it is desirable to have some indication of the liquid level in the tank . a liquid level gage ( sight glass ) 64 may be attached to the tank end wall 32 for viewing by a person standing or kneeling in the clearance space 60 . oil in initially drained into the oil storage tank 24 through a pipe 66 that extends upwardly from the tank top wall 34 in proximity to the end wall 32 . a funnel structure , not illustrated , may be connected to the pipe 66 via a flexible hose , whereby oil is drained from the vehicle crankcase into the funnel and eventually into the oil storage tank 24 . the tank may also be provided with a vent pipe near the end wall 32 ; the vent pipe is not visible in the drawings . the clearance space 60 enables the mechanic to reach or observe various mechanism , including the aforementioned drain opening 62 , sight glass 64 , and oil intake pipe 66 . all of these mechanisms are arranged at one end of the oil storage tank 24 , leaving the entire upper surface of the tank free of obstructions that would interfere with placement or use of the catwalk sections . the sectionalized catwalk provides a flat planar walk - on surface that is free of any projections or gaps that could be a safety hazard . from a description of the embodiment set forth herein , it is recognized that the invention also contemplates using the storage tank structure for the storage of new oil so that a motor operated pump , not shown , connected to the drain openings may be used when it is desired to pump fresh new oil into the crankcase after the spent used oil has been removed therefrom into a separate tank to complete servicing of the vehicle . having thus described the present invention by way of an exemplary embodiment , it will be apparent to those skilled in the art that many modifications may be made from the exemplary embodiment without departing from the spirit of the present invention or the scope of the claims appended thereto .