Alfie, I buy it from Karcraft in a 4L tin. I'm sure other vendors sell it too, it comes from Minispares UK I think.
SC850, the fitting is a brass valve cap, with OD machined parallel. It is gas torch soft soldered into a 1/8 BSP brass fitting, with Mini brake hose screwed in. Sealing is the standard rubber ring from said valve cap.
The other hose is also a Mini one, the 2 are joined by some pipe and a flare nipple. When this is loosened the end hose can be screwed onto the hydro valve. Before doing this I give it a pump to fill the lines. Then tighten the nipple.
Every 10 pumps I top up the cylinder. Next time, I'll use a Clubby one with the big plastic reservoir, it's easier to fill and holds more.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
