But dont they start with max fuel? do I have to drag them then take some of the fuel they start with?

Any class you designate as a tanker (which you should do for harvesters) only starts with 10% fuel

Steve

Wouldn't 10% fuel on a tanker sort of defeat the purpose of a tanker?

Well not if you build the tanker to fetch fuel from somewhere else (such as a harvester or dig site). As I just did in my game actually.

As Rabid_Cog pointed out the amount of fuel can be so large that its a good idea to place it directly under player control, rather than auto-filling them.

I actually think it's when they're marked as tankers. That is, I know it does it for tankers, I can't say for sure it doesn't do it for ones with harvesting modules.

Wouldn't 10% fuel on a tanker sort of defeat the purpose of a tanker?

But dont they start with max fuel? do I have to drag them then take some of the fuel they start with?

I believe when they have harvesters on them, they are automatically set to 10% fuel.

Yes, it's better to create massive harvesting bases and tug them to gas giants, then have a tanker(s) siphon off of them to colonies - or even have your battle fleets refuel directly from them.

For true set-up and forget on asteroid mines, you can drop a mass driver to shoot everything you mine back home (or to Luna, then home, if you don't want to risk accidental orbital bombardment due to picking up too many mass drivers by mistake.) In fact, adding cargo holds to the asteroid miner lets you plop it down, mine, and pick up when everything's depleted.

I've had no luck setting up sorium harvesters to dump their fuel on a base/colony- I set the conditional commands to drop off fuel when it's full, but it just waits around at the colony, and I don't see a manual command to drop off fuel in the command list.

Well asteroid mining is pretty much exactly as much micro management as normal mining. Maybe even a bit less, since you only need to order the mining ships to their location and establish a colony. If you would use automated mines on the same asteroid you would need to transfer the mines  via freighters, which also have to return, thus making one more trip. The real pain about mining asteroids (via any method) is that the accessibility of the minerals declines (quite quickly in some cases) and you thus have to move camp quite often. Which is why I mentioned comets, which boast significantly more minerals than most asteroids, so you dont have to move the miners that often.

Sorium harvesting is not particularly micro either, just move the harvesters to the spot and set up a continuous tanker-trip to fetch the fuel.