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冷凝水排水管code要求安装 P-trap，没有P-trap的minisplit要加止回阀，防止空气被吸入 HVAC 系统，避免出现水溢、霉菌滋生和系统效率降低等问题。冷凝水连到下水管是code明确禁止的。不知道楼主在哪里local code是哪国的，美国的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.