有一回，一封告密信送到武则天手里，内容竟是告发周兴与人联络谋反。武则天大怒，责令来俊臣严查此事。来俊臣，心里直犯嘀咕，他想，周兴是个狡猾奸诈之徒，仅凭一封告密信，是无法让他说实话的；可万一查不出结果，太后怪罪下来，我来俊臣也担待不起呀。这可怎么办呢？苦苦思索半天，终于想出一条妙计。

    他准备了一桌丰盛的酒席，把周兴请到自己家里。两个人你劝我喝，边喝边聊。酒过三巡，来俊臣叹口气说：“兄弟我平日办案，常遇到一些犯人死不认罪，不知老兄有何办法？”周兴得意地说：“这还不好办！”说着端起酒杯抿了一口。来俊臣立刻装出很恳切的样子说：“哦，请快快指教。”周兴阴笑着说：“你找一个大瓮，四周用炭火烤热，再让犯人进到瓮里，你找一个大瓮，四周用炭火烤热，再让犯人进到瓮里，你想想，还有什么犯人不招供呢？”来俊臣连连点头称是，随即命人抬来一口大瓮，按周兴说的那样，在四周点上炭火，然后回头对周兴说：“宫里有人密告你谋反，上边命我严查。对不起，现在就请老兄自己钻进瓮里吧。”周兴一听，手里的酒杯啪哒掉在地上，跟着又扑通一声跪倒在地，连连磕头说：“我有罪，我有罪，我招供。”

    Once, Wu Zetian received a letter which informed against Zhou Xing. The letter aside that Zhou Xing was plotting a rebellion in collaboration with others. Wu Zetian was furiously angry when she read the letter, and immediately ordered Lai Junchen to deal with the case severely. Hearing the order, Lai Junchen had misgivings about it. He knew that Zhou Xing could not be forced to tell the truth merely by using a letter informing against him because he was very sly and crafty. Lai Junchen also knew that he would not be for given if he should fail in dealing with the case, because the empress would certainly blame him and punish him. How could he solve the problem then? He turned the problem over and over in his mind, and finally thought out a "brilliant scheme".

    Lai Junchen had a sumptuous feast prepared, and invited Zhou Xing to his home. The two of them urged each other to drink, and they talked while drinking. After the wine had gone round three times, Lai Junchen pretended to sigh, "When Ihandle cases in ordinary times, I often com across prisoners who stubbournly refuse to admit they are guilty. I wonder if you have any effetive measures." Hearing this, he took a sip of the wine. Lai Junchen immediately pretended to be very earnest, saying, "Oh, please do tell me at once." Smiling insidiously, Zhou Xing said, "Get a big vat, scorch it hot with charcoal fire all around, and then let the prisoner come into the vat. Will the prisoner fail to make a confession of his crime?" Hearing this. LaiJunchen nodded his head in approval repeatedly. He then ordered his subordinates to bring a big vat, and had a charcoal fire lit all around it as Zhou Xing had said. He then turned to Zhou Xing and said, "Someone in the imperial court has informed against you, saying that you are plotting a rebellion. The empress has ordered me to deal with the case severely. So I beg your pardon, but would you kindly step into the "Someone in the imperial court has informed against you, saying that you are plotting a rebellion. The empress has ordered me to deal with the case severely. So I beg your pardon, but would you kindly step into the vat?" Hearing this, Zhou Xing dropped his wine cup to the ground and the cup broke with a crash. Then he knelt down with a flop, nodded repeatedly and said, "I am guilty. I confess I am guilty."

    This story appears in A General History as a Mirror of Past Events by Sima Guang of the Song Dynasty. From this story, people have derived the set phrase "kindly step into the vat -- try what you have devised against others".