If using PBW shorter soak times are highly recommended as I have also heard of peeps etching glass with it. The heated ultrasonic cleaner should outperform a sous vide as it warms the same but also has ultrasonic waves to help.
I have also not had any success with ISO on scorched/charred bangers and find SimpleGreen works pretty well but I would use DC cleaner if it was available here in Oz (and was cheap enough) as many have said how good it is here on the forum.
I plug the bong outlet with a silicone plug, fill the bong with iso or SimpleGreen, and stand it upright in the bath, the waves will travel up out of the cleaner inside the bong to work its magic.