Answer:
   
   We don't know what you've heard, but what we've heard is that when it
   comes time for three men to "witness" a woman's conversion [involving
   nude immersion], what's commonly done is for the water's surface to be
   covered with a thick, opaque sheet with a hole in it, just big enough
   to let her head through while discreetly shielding the rest of her
   body.
   
   Anything else is probably just your warped imagination, and no, we
   still have no idea of what you're thinking, but you should be ashamed
   of yourself, just in case. And another thing, it's not true, so there!
   
   Actually, there is an urban legend regarding what you think. As with
   any urban legend, there is a spark of truth in it. Here are two
   explanations:
     * The myth derives from seeing Jews in religious neighborhoods
       hanging their "talitot katan" out to dry. This poncho-like garment
       is about two feet by four feet, has a fringe on each corner, and a
       hole in the center for the wearer's head, and it looks somewhat
       like a small sheet with a hole, and many people have vivid and
       warped imaginations.
     * There is such a practice, but it is based on a misreading of the
       Kitzur Shulchan Aruch, a poor source for information on mainstream
       halakhic opinion on sexual matters. Most consider the legend to be
       an incorrect practice. Nevertheless, the practice does seem to
       survive in some "fanatical" extremes of Orthodox Judaism, without
       Rabbinic agreement.