I don't wash or rinse my slurries. I simply divide by eye by pouring intpo 2 sanitized plastic containers with snap on lids.
+1 - I saw no appreciable benefit when I rinsed my slurries.
in full disclosure however, I do have the ability to dump trub, dead yeast and other waste during high krausen which probably means less junk in my slurries.
I have conicals as well, and do pull from the middle of the slurry. But when I was using carboys full time I found the same as Denny, washing didn't make an appreciable difference. That said, I was never using more than 3 or 4 generations. If you go higher than this I think washing becomes more important for removing dead cells and trub.