I did not read this whole thread, but wanted to jump in and say that REAL swim diapers - i.e., the ones that are NOT disposable, actually DO hold fecal matter in. When fitted properly (snug against all openings) they work very well. I've been in waterbabies with both my children since they were 4 months old, and have seen on many, many occasions where swim diapers have successfully kept the pool from being drained due to contamination.
It is when parents use the disposable ones that there is a problem, because those do absolutely NOTHING.
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http://www.swimoutlet.com/Kids__Swim_Diapers_s/354.htm)