We built a container to let us filter and reuse oil when we need to drain a reservoir - typically during an annual reservoir PM. The unit has a pump and motor that runs on 110 volts, holds 275 gallons, and was constructed to be moved with a fork truck.

The oil in the reservoir is pumped into the container through a filter (we use a 6 micron 40CN housing – double-length Parker filter). While the reservoir is being cleaned, the valves on the unit are arranged so the oil is circulating through the filter. After the reservoir is cleaned, the oil is pumped back into it, through the filter. This simple unit has saved thousands of gallons of oil since it was built 20 years ago.
The container has a big door and the interior of the tank is epoxy-coated for easy cleaning - the residue from the oil does not stick to it. After use, we wash the interior with water. The drain at the bottom is large and the water drains quickly. We then put an air hose into the tank for about 30 minutes, change the filter and it is ready to go again. 
If I had to rebuild this unit I would probably use stainless steel for the tank and piping. When water is used in an oil application I like to use stainless. I would also use the biggest motor and pump that would run on a 15 amp 110 volt power supply for more GPM and therefore quicker turn around. This unit is almost always used on hydraulic units as the tank is not big enough for most lube units we have here at the paper mill. We have 8 paper machines 3 power boilers a wood-yard, waste fuel area and a big paper converting area, so the opportunities for this unit are numerous.
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