I plan on using a forstner bit and use a regular airlock with bung. I don't ever get a good seal with the little ones. By the way, the containers held citric acid before. I used them last year for the bigger batches, now they are little batches. Next year the 32 gallon Brutes will be little batches.
As a side note, my estimates of harvest were actually pretty close overall to actual harvest. I am tracking each vines harvest weight. It is a bit more work, but it will help in the future for pruning decisions and cluster thinning. The one that I was way off on was the St. Pepin. The actual yield was much higher than estimates. Frontenac is running just a tad on the lower side, but that is because of incpmplete cordon development this year. There were a few missing arms here and there. As a result, the newly formed cordon had two clusters on it as opposed to 24-30 clusters(dropping overall yield). I didn't expect a huge yield- these were third yearvines. A lot of growers don't even take a crop in the third year.