I've been saving yeast yeast for a while now... my standard practice is, throw a jar or two in a 5 gallon bucket of start san, you yourself, scrub in.. by that I mean I'm washing my hands in the bucket of star san...Rack you brew to the keg, have a spoon, sanitized, with a long handle, scrub in some more, then take out the jars, empty, I will let them drip for a minute, then scoop some yeast off the yeast cake... I don't go to the bottom, rather skim off the top. Then I will pour an inch or a bit more of some hoppy brew on top to create a cap.. Some Saran Wrap, put the ring on it... Into the fridge..
Wilco, I'd put some Saran Wrap on that jar, then a rubber band... My fear would be to forget about the seal the lid will do when I take it out to warm up.... KER POW!! I'm erring on the side of caution.. Sneezles61