Tubs

1. There are fixed and free valve extenders.
   
   

For the fixed extenders you remove the valve core, add the extender, then put the valve core in the extender. If you use these you must have them in place before you mount your tub. It can't be done after the fact. They leak, too, unless you use plumbers tape on them. I think they are shite.

The free extenders, like the Topeak ones which I recommend, simply screw down on to the exiting valve stem. A nifty little insert inside them interfaces with the core allowing the extender to open and close the core. You screw down the extender, use the extender to unscrew the core, pop the pump on, do your business, pop the pump off, use the extender to close the core then remove the extender. You only need one, and you carry it with you on your ride.

There's also the extenders like the Zipp ones which are just a tube. You jam open the valve nut on the valve stem, and then fit the extender on the threading for the valve cap.

Then there's the fourth option, which is the Vittoria red valve. You take the whole of the valve off, leaving a threaded stub on the tyre with a silicon sealing ring, and replace it with an entire new, longer, valve. Not all Vittoria tubs have the red valve system - the Corsas do, the Pistas don't - they have standard removable cores.

IME the key to any of them is to make sure they seal. I've never had a problem with the Vittoria red valves not sealing, and for the others I use a bit of Loctite 542 sealant on the threads. I've never used a Topeak extender in anger, but I do carry one in my saddle bag in case I need to use my spare tub.