Then best and only sure way to tell whether your prints are thoroughly washed is to get a test kit for hypo and test for residual fix. Very easy to do and very inexpensive. All other ways are a waste of time and money not to mention water for those of you who are washing for an hour or more. Lex uses the simple method that works very well. A couple changes of water and voila, done. How archival do you want your prints? 100 yrs? 500 yrs? or is 10 yrs ok?