A method of depositing an extrudable substance onto a surface. The method comprises the step of delivering the extrudable substance from a cartridge to a flow-bypass assembly. The method further comprises the step of selectively controlling the flow-bypass assembly to purge air from the extrudable substance before the extrudable substance enters a delivery tube. The method further comprises the step of selectively controlling the flow-bypass assembly to deliver the extrudable substance from the flow-bypass assembly to a valve assembly via the delivery tube. The method further comprises the step of controlling flow of the extrudable substance from the valve assembly to a nozzle.