You have two unrelated things there. The line between injectors should continue to a small plastic nipple at the top of the fuel tank, as you described for the Deutz. On some later models, it feeds the Thermostart reservoir before getting to the tank.
And the other, larger fitting is the Thermostart, a pre-heating device similar in function to glow plugs. Internally it's about the same as a car cigarette lighter, a coil that heats when electricity is applied by turning your key to the left. There should be a tube down from the Thermostart reservoir, a small plastic bottle mounted up by the top radiator hose, that you fill with diesel.
When the Thermostart heats up, after some 10 seconds it allows fuel to come down that tube and into the intake manifold. Then after a moment the heating element ignites that fuel inside the manifold.
Thermostart is a cold weather option, not essential in a mild climate. Looks like your prior owner didn't need it.
Here's a post I made long ago with photos showing the Thermostart fuel vapor, then flame.
Hoye later used these photos in their description.
By popular demand, (Well I think it is interesting :D ) I just took these photos. Incidentally this was with the key in 'Start' position but with the clutch safety switch preventing cranking. I was testing to see if TS operates in Start position as well as when the key is cranked left. Vapor...
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