Try a better plumbing merchant thats about all I'd comment on. Even seen em in B&Q.
Cable operated not springloaded
Controlled from a single lever with double action throw on two levers at the back. made by morse.
This was how I rigged mine other people may do it different.
Full forward scoop down gate closed
Neutral Scoop up gate closed (holding water in tank)
Reverse scoop up gate open
when you dont need it I used to keep it in reverse
Takes bloody hours to work out the cables and adjust end lenghts to get it to work right.
Alternatly have two levers one open close gate othe lever fill. quicker to set up but more difficult to operate & keep in synq
Edit: work out you cable extension before connecting it to the gate valve
Measure your cable extension/ Travel first. Then work out the arc to open close the gate vave drill handle on gate valve at a point where that extension will give you full operation of the gate valve.. not rocket sience and there is lots of adjustment on the cable ends. but if you get it close to start with its much easier
