From China Digital Space
喝茶 (hē chá): drink tea
Euphemism for police interrogation. When invited to “tea,” one is asked about their political activities and warned against further involvement. Those compelled to attend these tea sessions is said to have been “tea-drinked.”
In July of 2014, author Murong Xuecun issued a “statement of surrender” to Chinese authorities as an expression of solidarity with friends who were detained for attending a weekend gathering marking the 25th anniversary of June 4th, 1989. Several days later, the outspoken novelist was asked to tea by the local police in Beijing:
Huoguangweiyu (@火光微语): @郭玉閃又日 Brother Murong Xuecun “surrendered” himself to the police. Today, he was summoned to the Purple Bamboo Park police station for questioning at five in the afternoon. He's still drinking tea with the police, and I'm waiting for him at a bar outside the station.
See also check the water meter.