I recently decided to really learn the right way to rehydrate. I found this link with expert advice.
http://koehlerbeer.com/2008/06/07/rehydrating-dry-yeast-with-dr-clayton-cone/
Btw, on page 80/81 in the third edition of Charlie Papazian book, the complete joy of homebrewing he describes the process. I than read in the book, Yeast, by white and Jamil that often an expert will advise to just sprinkle yeast on the top of the wort and add more yeast because the beginner might not have down a proper sanitary process. he describes,
1. Warm the dry yeast to room temp
2. In a sanitized container , prepare an amount of sterilized tap water at 105 degrees, f (41c) equal to ten times of the yeast.( 10 ml/gram of yeast)
3. Sprinkle the dry yeast on top of the water. Trying to avoid setting up large dry clumps. Let sit 15 minutes , gently stir.
4. Once the yeast has reconstituted, gently stir once again to form a creme, let sit five more minutes.
5. Carefully and slowly , adjust the temperature of the yeast to within 15 degrees F, (8 c) of the wort temp.
6. Pitch the resultant creme into the fermentation vessel, ideally as soon as possible.
That book goes on with more detail on the why and also discusses using go-ferm, bio available nutrients and about how to avoid yeast mutants and death of the yeast cells. Temperature is stressed as very important. Cold water in yeast rehydration can kill half of your cells.
I hope this helps. If your very curious into the how and why read the yeast book, if you just want to get her done , follow the Papazian book.
I followed the process above and I had to use the blow off tube. In the bottom of the jar of sanitizer containing the blow off tube as a very lovely thick layer of creamy yeast.