yeah I dont know either. But to be a quart short seems like a lot, I dont know if there is sludge in there. But if you are pumping two in and it comes out the top hole, it would lead me to beleive its not all coming out

I drain the lower units over night then trim them all the way up. Let them sit about an hour, then trim back down. I'd say another 1/2 pint or so drains out after trimming them back down.