After listening to the show a couple weeks ago Chad mentioned cold crashing while still in the carboy before transferring to the keg. I usually transfer and crash in the keg, but I gave this a try on the last two batches. As the gas in the headspace and blowoff tube cools it contracts and creates a vacuum and starts to suck the starsan up the blowoff tube toward the carboy. I caught it the first time about half way through cooling but it still sucked a little starsan into the beer. This time I am taking it down 10F at a time (70 to 40) and I am able to empty the blowoff tube back into the container with the starsan in it at each step and keep it from being drawn into carboy. The little bit of air that is let in each time I do this is still lighter than the CO2 blanket in the carboy and does not get to the beer, I would think.
I've never been able to figure out the trick of drying off the carboy rubber stopper after soaking it in starsan - it always seems to work it way out of the glass neck, so lately I've just kept a 1 1/2" blow off tube for the entire 7-10 days before moving things over to a corney keg. Is there a snap clip that would help the rubber plug stay in place?
