Trying to remember
Since you mention a tube, I'm assuming you have a mechanical gauge. If so, I believe all you have to do is purchase another piece of tubing that's capable of withstanding 100 PSI (just in case) and some additional fittings to make the connections.
I would suggest home depot or auto parts store. If no luck, try looking for the type hose you need at McMasterCarr.com.
Good luck.