In this case my tug wasn't a true tug, it was a makeshift design, a freighter with a tractor that was rushed out to try and save a smaller freighter type that had run into difficulties (but which ended up exploding due to a maintenance failure anyway) and was designed for a fast refit. I chose the freighter in question as it was one of my largest ships, and would therefore be least affected by the addition of more weight, but it was by no means a specialised tug with great pulling power. It was designed in a pinch to move relatively small vessels. In this case, with the low fuel situation, I did end up equalising fuel, but it would be nice to be able to tow it back for RP purposes (since the two ships were from two different factions - the out-of-fuel ship was transferred to the NSA in order to be rescued, but it wasn't actually their ship).