My stager is a gardena type connector with the spring removed and arranged so the spring pushs it open. It’s held closed by the pressure of the first stage inflating a bicycle inner tube against the inside of a pvc pipe connected to the ring of the connector.
On removing the pipe I found unsurprisingly the inner tube had got wet from the first launch. The water acted as a lubricant between the inner tube and smooth PVC pipe. I need to add a ridge to the inside of the PVC pipe which I was going to do originally but skipped it since it had such a good grip without (dry of course).