一口清

yīkǒuqīng ㄧ ㄎㄡˇ ㄑㄧㄥ

    • able to explain complicated accounts or matters clearly in one breath

Character by character

Saying俗语俗語

Idiom惯用语 · Rarely used now

Literally
clear in one go
Meaning
Able to explain complicated accounts or matters clearly in one breath. Approving.

Sources