I've only ever heard the "best is 5, no greater than 10" under mechanical vacuum. I recall reading somewhere that although more difficult, you can create vacuum on 5/16" but needed well over 60 taps (thinking 80+?)to create the volume of flow needed for the sap to create a proper column in the tubing. On 3/16" the number is around 30 iirc.
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2023 -30 trees -24 vacuum, 6 buckets. ~1,845 L sap; Syrup count: 49.25L
2022 -30 trees -24 vacuum, 6 buckets. ~1,530 L sap; Syrup count: 48.65L
2021 -29 trees -23 vacuum, 6 buckets. ~1240 L sap; 34.5L of syrup
2020 -30 trees 32 taps. ~900 L sap; 27.1L Syrup.
2019 -27 trees 31 taps. ~725 L sap; 22.2L Syrup.
2018 -19 Trees 20 taps. ~750 L sap; 18 L Syrup
2017 -4 trees 4 taps. ~60 L sap; 1.5 L Syrup