Abstract: Surplus moisture drain of air conditioning apparatus comprises a U-shaped trap in which a water seal is operatively maintained to prevent air flow along the drain, and an air break on the outflow side of the trap comprising a delivery spout with a tundish in spaced relationship below it to prevent siphonic voiding of the trap, the components forming said trap, spout and tundish with associated pipework all being formed of borosilicate or other stable corrosion resistant glass coupled together by releasable compression couplings.