Ok... I have cobbled together an idea in my mind for a pressurized coolant
system with relatively easy recovery. Two tanks. One is a pressurized tank
for coolant with a pickup near the bottom of the tank. (Also a large drain
for flushing). The other is a collection tank for run off from the machine.
A large filter assemble keeps chips out of the recovery tank. When the
recovery tank starts to get full you close a valve from the filter, open a
valve to the pressure vessel, and the pressure equalizes allowing the
collected lubricant to flow into the pressure tank. When done just reverse.
Close the valve between the tanks and slowly open the one from the filter.

A little crude experimentation has shown that relatively low pressure and
volume is needed to work a rig like this.

You do not even need a fill port on the pressure tank when coolant runs low.
Just pour it into the recovery tank. Air pressure does the work. My
thoughts are that with pure oil based lubricant coolants (can't use a water
based on my mill) there is no risk of ignition. No vapor or mist with a
liquid stream, and no potential ignition source as part of the coolant
system like a pump motor.

My concerns are what materials easily at hand to use for the tanks.
Obviously would need to be impervious to oil, and other petroleum
distillates and water displacers. Also, not likely to fail
catastrophically. I'm thinking aluminum or steel. I would be open to other
ideas for materials. I would probably have to make the tanks to size and
area available.

I know I am probably re-inventing the wheel here, but it's a fun mental
exercise if nothing else.