The pumping mechanism in multi‐inlet microfluidic channels usually requires multiple micropumps to be separately attached to each inlet. Unfortunately, this may create fluid leakage resulting from a considerably high internal pressure. To address this, a passive sub‐atmospheric pressure‐inducing micropump is proposed and its performance is characterized as a function of the flow rate and the gauge pressure. With this pump, a sufficiently high flow rate is generated, comparable to some active‐piezoelectric micropumps. The gauge pressure is exponentially descending with time and can be crudely classified into three regions of high, moderate, and slow pressure‐release times. Overall, the stabilized pressure is identified within 70 s < t ≤ 300 s for slow rate mixing while rapid mixing is applicable at t ≤ 70 s.