By putting a hopper into any side of a brewing stand and putting water bottles in the hopper, the bottles fill the stand, or at least they should.
They do the first time, but then when the bottles from the stand are removed, new bottles don't flow back in when there is a hopper underneath (even if the hopper is full or powered)
Steps to reproduce:
1. Place Potion Brewer
2. Place hopper(A) going into any side of the brewer
3. Place a hopper(B) underneath
4. Place a redstone block underneath hopper(B)
5. Fill hopper(A) with water bottles & they will flow into the stand
6. Remove redstone block from hopper(B)
7. The 3 original bottles will empty into hopper(B) but no other bottles will flow from hopper(A)
8. Reloading the save fixes the issue once
9. Even if the hopper draws just one water bottle out of the brewer, that one slot will not be refilled.