I have krausened many batches. You want to use either the same yeast you did it with originally or with something neutral (US-05 has worked for me if I don't have any yeast left from the batch). Basically, you want to get something up to high krausen and then put it in the keg, you don't need a ton of it but it does need to be active and moving. If you use a different yeast, you might have it attenuate down lower than the original yeast would have and change the profile of the beer.
I usually do something like half a liter of wort @ 1.035 and some yeast, give it an hour or two to get going (krausen is up) and then dump it in.
You will get some junk in the bottom of the keg but it will come out in a few pints after it all drops out.
Also, you won't need a blow off tube. In fact, you can just seal up the keg and let it carbonate naturally from the yeast's action, just make sure it doesn't get too crazy high.