yeast harvesting

I've been yeast harvesting for awhile and currently boil the Bell Jars prior to collecting and washing the yeast. I was wondering if it is really necessary to boil the jars. Star San seems to do a good enough job during the brewing process so why wouldn't it do just as good during the yeast harvesting process. Any thoughts or good/bad experiences with not boiling?

I typically use a pressure cooker to sterilize the ball jars filled with water.  I then use the sterilized water for rinsing the yeast to remove the trub.  I get about 5 to 8 generations of clean yeast before dumping or seeing anything unusual with the harvested yeast.

I have short-cut the process by occasionally using a sanitized ball jar, but quickly found that after 2 to 3 generations, I will get some stringy material forming in the yeast which I am sure is bacterial contamination.