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An "upstand" means either one of two alternative arrangements of water fittings to prevent backflow by backsiphonage:
Type A upstand - An upward flowing supply or distributing pipe surmounted by an anti-vacuum valve (Type DA), or an anti-vacuum valve combined with a single check valve (Type DUK1), any part of the outlet of which is located not less than 300mm above the spillover level of an appliance.
Type B upstand - A branch pipe serving an appliance, where the height of any part of the branch connection to the vented distributing pipe is not less than 300 mm above:
a. the spillover level of the appliance; or
b. the highest possible discharge point served by the vented distributing pipe, whichever is the highest.
Interpretation given in Regulators’ Backflow Specification - backflow prevention arrangements and devices: terms relating to backflow prevention