I decided to email support at SSBrewtech and this was their response.
Gordon,
This happens with all air tight fermenters, as the liquid cools it contracts, so it can draw in outside air or in this case sanitizer. I would recommend going to an airlock or bubbler during crash cooling, that way just air and not sanitizer get drawn into your Bucket.
No need to worry about oxidation, there is still the protective blanket of CO2 on top of the beer. Thanks!
Cheers,
Michael
So basically what he is suggesting is to use the typical three piece air-lock with no liquid inside. I will try this with my next batch and see how it goes. I typically use a blow-off tube for the first three days and then move to the airlock after the first big push.