I'd remove those check valves as well TD, those lines should be clear to drain with no restriction. Back when the Green Leakers were common it was not unusual to find one fitted with a slobber drain tank. I worked on a fuel tanker at the airport here in Knoxville, well, actually the airport is in Alcoa TN, a couple of miles from Knoxville, that had a 6V-53 that had a factory fitted reservoir that the air box drain tubes drained into. Obviously, it's not desirable to have an engine slobbering oil all over airport ramps.