Contacted Hamilton company, and they do not recommend any external flow because it alters the internal flow of the circuit. 1L/min external flow = 16.6cc/sec extra flow to circuit. When external flow is added in excess, the machine may stop internal flow (circuit) delivery. Apparently, other users of Galileo vent have run into similar issues when trying to setup continuous nebulization to vent. Hamilton is working with the company that makes the aerogen nebulizer which is similar to ultra sonic neb, but doesn't add extra flow to circuit.