I don't know about the vinegar soak. Honestly, I don't know that I've ever had embroidery thread/floss bleed. Even pieces I worked on 40-50 years ago, when washed, did not bleed. I would suggest a light wash in a tub or sink with cold water and a bit of Dawn liquid dish soap. Just swish around a bit then rinse with cold water as well. And to dry I would gently squeeze, just by pressing flat in the tub/sink most of the water out of the piece and then roll in a towel. Let stand in the towel for a bit until it absorbs most of the water then continue to dry by laying flat. Iron from the back side.