Being a "VMR" skipper in NSW our group was normally told that the vessel owner (or controller) must attach the tow line.
Its all sorts of insurance issues. If the rescue boat crew attaches it and it damages the stricken vessel who is to blame. If the line strangely detaches from the stricken vessel and it gets washed into the rocks or hits another boat who is to blame etc etc
There is so much crap that goes on. We were not meant to attach the towlines to the other boat, however i was often giving advice to the sticken boats as some of them had no idea. Almost holding their hands. Sometimes its almost easier to attach it yourself (wink wink) Luckily most jobs we did were in mostly calmish water. Rough weather jobs need (unofficial) improvisation to get the job done, or enough to tow into calmer water and re-rig/re-position towing lines
The best results we normally had was using a bride, attached to each corner on the stern with the tow rope secured RIGIDLY in the middle of the bridle. The sliding tow rope idea looks good, but once it slides to one side it tends to pull that stern quarter of the rescue down into the water. Every boat will react different and there are many ways to do it. Im not saying this is the best way.
We have towed vessels such as 20" Bayliner bowriders @ 20 knots with a 7m Sharkcat in the calm. Different story in the chop !As a side note it is interesting being pulled across the bay at 40 - 50 KM/H in 20 knt + winds
cheers
Rod