In reply to BoulderyDave:
With same diameter ropes, I usually tie just a flat overhand like everyone else does with 30cm tails.
With different diameter ropes, I sometime use the "Doppelter T-Spierenstich" (Double T-Fischerman's Knot) shown here
http://www.gudelius.de/spst.htm (you have to scroll down a bit)
Basically it's a double fisherman's knot but is not tied "inline". It's tied as a "flat knot". It's more complicated than the overhand knot but non more complicated than the regular double fisherman's. It's not much more bulky than two overhand knots. I've found it to be relatively easy to untie after loading. I've never seen or heard of it capsizing.