Acerbis tanks come with their own dual petcocks. I've got the one that is almost 6 gallons. It was easy to install, but you have to relocate or raise your stock turn signals. It has held up well.
I fairly anal about bike maintenance and keeping things tight. A month or two after I posted this my Acerbis began to leak near the backbone, so I switched to a Clarke. It holds a gallon less, but it feels better between the knees.