A filter unit for a mixing apparatus includes a hydrophilic filter and a hydrophobic vent filter. The hydrophilic filter is configured to receive a fluid including a liquid and gas. The hydrophilic filter is further configured to sterilize the liquid. The hydrophobic vent filter is configured to receive the gas from the hydrophilic filter. The hydrophobic vent filter further includes a vent and a membrane configured to separate an interior of the filter unit from an exterior of the filter unit, the gas being vented from the filter unit by flowing across the membrane and out of the vent. In some embodiments, the filter unit further includes a defoaming device configured to receive gas, foam comprised the liquid containing trapped gas, and some of the liquid from the hydrophilic filter and is further configured to release at least some of the gas from the foam.