Originally Posted by zonatandem

Been using that type of system since the early1970s when braze on mounts were rare. Used to have a double mount on my PX-10 for long events.
Currently, on both tandem and single bike, we utilize a Minoura handlebar mount.
The bottle's cap has the little pop-up plunger removed and a plastic drinking straw is inserted. No need to remove bottle to drink; dip your head down and sip away!
The 'straws' are plastic tubing bought at hardware store that fit properly and cut to your desired length.
For pilot we use a stiff/non flexible tube; for stoker a bit longer flexible tube so she does not bop her head into my butt when drinking.
This had worked fine for use for over 3 decades.
Pedal on TWOgether!
Rudy and Kay/zonatandem