Checking wash

[HodyMac]

Newbie here. I’ve got a batch of Deathwish Wheat Germ fining on day 6. One bucket still bubbling, the other has slowed way down.
I’ve read about checking SG but doesn’t pulling the lid off the bucket off kind of defeat the point of an air lock?

Is that what you do? Pull the lid off and if the SG is still high just put it back on?

Like I said, newbie.

And along the same lines, I’ve read people are fermenting in Brute trash cans. How do you keep the air out? Just the trash can lid?

Thanks!