Hope this finds everyone safe, fed and healthy. I need some process advice. I'm using a lager yeast (Imperial Global) in a Baltic Porter, fermenting at 53º and now at nearly 4 weeks. It was a good-looking fermentation. Now, I want to take gravity readings to be sure it's at my target before I a.) raise it to 56º for a few days of diacetyl rest and then b.) gradually drop it down to 35º (the advice of the folks at Imperial) for 6 weeks. I'm doing everything in primary, using a cylindro conical fermenter (The Catalyst). But I have yet to install a sample port. As much work/time as this little experiment is requiring, I don't want to potentially screw this up by introducing too much O2 before starting to lager. I'll draw my samples out of the blowhole, replacing the plug each time of course. If this was your batch and given that fermentation is probably nearly done, would you a.) assume it's close enough and not sample; b.) sample and don't worry about it; or c.) purge with CO2 after each gravity reading (assuming I only need two) before moving ahead? I don't have a CO2 setup and probably wouldn't use it enough at this point in my brewing to justify buying a 5-gal. tank. So if the consensus is that I should purge, I'll probably just bottle after the rest, install a port and sample things that way next time. Thoughts, please?