Pumpdown predictability of large pipe-type vacuum chambers is improved through design tradeoff reevaluation based on checkout anomaly analysis. Truncated-cone pipe chambers up to 2000 ft long and 200 000 ft3 in volume, which served as underground nuclear effects testbeds, were analyzed. Inconsistencies in evacuations to a base pressure of 1 mTorr are identified with the sorbing time variable of the chamber wall and experiment support materials. Variations in pressure levels along the pipe chambers are shown related to configuration factors and to design tradeoffs on allowable inleakage from concrete shrouding, sand stemming, and tunnel atmospheres. Cascading graphs innovated for tradeoffs include two recently derived flow conductance equations.