On Tuesday, September 11, 2012 4:23:08 PM UTC-4, DerbyDad03 wrote:
Why would a clogged vent cause water to be sucked out of multiple
traps during the time we were at work?

By itself, it wouldn't, but it would "seal" your drain system and allow some other event downstream (maybe related to opening a manhole) to suck your traps, which shouldn't happen if the vent is NOT blocked...