If your taps and drops are 5/16 and your tubing enters the bucket but does not extend below the sap in the bucket, don't worry, the sap can and will pass the gases (looks like air) in the tubing. However, if you use 3/16 tubing the sap will not pass the gases and it can form a slight vacuum. On buckets this is not generally considered good unless the fall from the tap to the bucket is more than just 2-4 feet. If you have a side hill with the bucket 5-6 or more feet below the tap, you can produce a little vacuum but when the tree freezes again it will pull sap back in thru the tap unless you use CV taps.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.