Fitting heater to a Vario

I am nearing completion of our Vario conversion and fitting Diesel heater.
I have made a hatch above fuel tank to gain access for connecting fuel pipe.
Option 1 - disconnect pipes and somehow remove sender unit, drill hole in top of tank and fit separate pipe.

Or this, possibly looks promising, that Mercedes have provided spare nipple on sender unit ? See photo, anyone know if the nipple can be cut and connected to for heater ?

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Hi Grape
Not sure what I am looking at, I can't make out where the pipe with the rusty nut on the left goes.
The 3 wavy lines mean cab heater, so I think that is the very thing, but don't know why it has a return.
Searched for answer to this for ages, but have just found page, seems sender is fitted to many different trucks and nipple is for night heater