This is a Surge & Recovery Combo Tank for 1988-1998 GMT400 trucks with Mild Slosh Tubz. 

The primary tank is the engine coolant surge tank - equipped with a pressure cap and to be used where the radiator does not have a pressure cap. It is set up with a -6AN Upper fitting and -10AN Lower fitting. 

The second, smaller tank on front is the coolant recovery tank. As the pressure cap on the Surge Tank lets off pressure (and possibly some coolant), it will flow directly into the recovery tank on the front. Once the system cools and the coolant level drops, the surge tank will create a vacuum and pull the coolant from the recovery tank back into the system. The recovery tank is equipped with a -4AN fitting which plumbs directly to the pressure cap on the surge tank, and a screw-in vent fitting on the top. 

This tank is in the bargain bin for only one reason:

1. Apparently, I wasn't paying attention when I welded on the -6AN upper fitting on the surge tank - the weld is fine, but it off center just enough that it belongs in the bargain bin. 

Both tanks have been pressure tested, and the reservoirs both function perfectly. The issue is strictly cosmetic. We can also have this tank powder-coated for additional cost.