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冷凝水排水管code要求安裝 P-trap，沒有P-trap的minisplit要加止回閥，防止空氣被吸入 HVAC 係統，避免出現水溢、黴菌滋生和係統效率降低等問題。冷凝水連到下水管是code明確禁止的。不知道樓主在哪裏local code是哪國的，美國的code基本都是相同的。

[M] 314.2.1.1 Condensate discharge.

Condensate drains shall not directly connect to any plumbing drain, waste or vent pipe. Condensate drains shall not discharge into a plumbing fixture other than a floor sink, floor drain, trench drain, mop sink, hub drain, standpipe, utility sink or laundry sink. Condensate drain connections to a lavatory wye branch tailpiece or to a bathtub overflow pipe shall not be considered as discharging to a plumbing fixture. Except where discharging to grade outdoors, the point of discharge of condensate drains shall be located within the same occupancy, tenant space or dwelling unit as the source of the condensate.