When my GSD puppy just had a week of diarrhea, I gave her nothing but chicken breasts and rice (both boiled) and then run through the blender with a little bit of warm water until it resembles a very thick porridge. I gave her this for about 24-36 hours until her stool firmed up again and then gradually added new venison kibble a little bit at a time. She had been on a grain free fish based kibble and it was not agreeing with her after several months.
As of today, she has solid stool again and the transition took about four days. I did a faster transition than mentioned earlier since I had already been fighting liquid stool and, once the chicken breasts and rice porridge got her firmed back up, I added a little bit more venison kibble with each meal until she is now getting a full portion of the new kibble.
Sabra - female GSD - born April 30, 2012
Sargeant - rescued senior GSD male/foster failure - approximately ten years old (August 2013)
Max - rescued GSD - Dec 22, 2010 to March 7, 2012 - at the bridge
Sable - rescued GSD - at the bridge