I have the tanker pack form Jointedrails and wanted to load one with Avation Fuel or Gasoline. I don't see this in the list nor do I see it as a product to download from the DLS.
How can I do this?
Aviation fuel and petrol (gasoline) are both built-in products:
Aviation Fuel,<kuid:-3:10045>
Petrol Fuel,<kuid:-3:10012>
You'd need to edit the config.txt for the JRPX tanker and add either/both of the kuid's to the product list for one of the loads (load1 would probably make most sense, since it has less products configured by default).
I suspect JR intended for the 'allowed-categories' config tag to allow the default liquid loads, unfortunately there's an annoyance (some might call it a bug...) whereby you can't specify both a product list AND a product category at the same time...
(There's also another bug where the specified allowed-categories are the inverse of the categories allowed, thus if you want to specify the liquid load category, you'd need to specify that 'container, general load, and bulk load' are allowed, leaving liquid load ommited from the categories allowed, but that's another story)