We do not currently offer this option on the product on the website. We do sell these items separately and they can be fitted by the client to the 6mm ID hose that comes with the backpacks.
I will be adding this as a cost option on the website but I have a slight glitch in the software that controls the website content which I am awaiting a software engineer to fix.
If you give our sales team a call on 01726 66400 they will be able to advise the cost of any add-on connectors or valves for these backpacks.