scavenging station. That's what I couldn't remember. Build one of those and assign someone to it and u get random extra junk and caps.
If anyone wants to set up a supply line between your settlements, which is easy to do, it shares your resources between settlements.
Go to a settlement, enter workshop mode, select a settler and then select Supply Line, then select the settlement you want the line to. This settler now walks a path connecting the two settlements.
The way it works is the settlements piggyback off eachother, so you don't want or can't have a supply line from all your settlements going straight to Sanctuary Hills, rather they all need to be connected together so you have Settlement A in a line to Sanctuary Hills, then Settlement B is in a line to A, and C to B and so on. When you're looking at your map in your Pip boy, you can view your supply line. This way you can see which settlement connects to where.
So here is an example of starting a supply line:
And here is another with more settlements, although this persons line is kind of retarded but you get the idea:
You need to have the LOCAL LEADER perk under charisma in order to unlock the supply line, I'm pretty sure.
Here is mine from a few days ago, I had to take two pictures since you cant zoom out fully, but I think my supply line makes a little more sense compared to the example I posted above: