My sorium harvesters have some limited engine capacity so that I can order them around without messing with tugs. Whenever they fill up, I give them an order to drop off 90% of their fuel at Earth, which usually takes 10-15 days, depending on alignment.
Jovian class Fuel Harvester 60,000 tons 275 Crew 1506.8 BP TCS 1200 TH 900 EM 0
750 km/s Armour 1-136 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
MSP 16 Max Repair 75 MSP
Intended Deployment Time: 60 months Spare Berths 0
Fuel Harvester: 19 modules producing 532000 litres per annum
Joachin Systems C300 Ion Drive (3) Power 300 Fuel Use 7.07% Signature 300 Exp 5%
Fuel Capacity 2,680,000 Litres Range 113.7 billion km (1754 days at full power)
This design is classed as a Commercial Vessel for maintenance purposes