Dunno what kind of oil they cook chips in where you come from, but what goes in my tank is a lovely light coloured golden liquid, filtered to 1 micron, which is more refined than what comes out of the pump on your local forecourt.
Are you seriously trying to argue that cooking oil is less viscous than diesel? And as I said, real diesel doesn't sustain bacterial growth in the tank/lines/filter.
Nope, but stating that your assertion that it has the viscosity of toffee is plain wrong. The action of filtering it to 1 micron means it may well contain less contaminants than pump diesel. The viscosity only becomes an issue in really cold weather, when mixing a small percentage of petrol in cures it. A mechanical Bosch diesel pump wont struggle to pump vegoil at all, so thats not a problem either. No particular risk of bacterial growth in the fuel system as the oil doesn't sit still or stay in there long enough to sustain it.
If it was a cause for concern, a small percentage of petrol or larger percentage of diesel mixed in would likely prevent it.
Its not something that I have encountered in tens of thousands of miles of WVO usage.
As you say though. Not really worth the bother if you only intend driving it a couple of thousand miles before getting shot of it.