[flbrewer]

When cold crashing I typically remove my airlock from the Speidel and cover w. foil. Would it better to just dump the sanitizer and keep the airlock in an effort to keep more oxygen out?

[Stevie]

An airlock without liquid is just a hole, same as the foil.

[flbrewer]

An airlock without liquid is just a hole, some as the foil.

damn you for pointing out the obvious.

[pete b]

An airlock without liquid is just a hole

This answer is an instant classic!

[Hooper]

If you were to look up and read about Pasteur's flasks, you might come to the conclusion that the the S shaped air lock is not quite a "hole"...You might also surmise that it gives no better protection than foil...but both would give better protection than a hole. I think maybe a piece of cotton in the open end of the airlock might help keep airborne particles out of your fermenter.

[Stevie]

If you were to look up and read about Pasteur's flasks, you might come to the conclusion that the the S shaped air lock is not quite a "hole"...You might also surmise that it gives no better protection than foil...but both would give better protection than a hole. I think maybe a piece of cotton in the open end of the airlock might help keep airborne particles out of your fermenter.

Correct as far as contaminates go, but they all work the same when it comes to incoming air. An empty 3-piece airlock would work fine too.

[blatz]

when I cold crash, I replace the airlock bung with a solid bung.  if you get a good seal, it also lessens your oxidation risk as you cool down, due to the vacuum. 

[russell]

 I have never thought about all this. I just keep the bubbler on with starsan in it. Does it help to just plug it up? I would think that air couldn't get into the carboy with a bubbler on it.

[JT]

IMO it has been a non-issue.  I cold crash in the same place I fermented, I'm not sloshing the beer around, so while oxygen may be getting into the fermenter, I don't think it's mixing much with the beer.  I guess if I get "oxydation" feedback from the Spring Swap or from my brew club, I'll take a harder look at it, but for now: no oxydation notes and no worries.
If I'm using a 3 piece airlock, I simply remove the inside water lock, and cover the lid with a bit of foil.  If I'm using an S-lock, I just crash it in place.