A needle assembly has a first body and a guide rod supported for sliding movement between an extended position and a retracted position. A second body is attached to the guide rod. The second body is relatively farther from the first body when the guide rod is in the extended position and relatively closer to the first body when the guide rod is in the retracted position. The guide rod is biased to the extended position. The second body supports a venting needle that extends beyond the second body by a fixed length. A liquid handling needle is coupled to the first body. Sliding movement of the guide rod toward the retracted position retracts the second body and the venting needle relative to the liquid handling needle.