请帮忙分析个英语句型The one thing that I dislike about tipping in the

请帮忙分析个英语句型
The one thing that I dislike about tipping in the U.S. is how sometimes the
restaurant staff forget that tips are supposed to be a reward for quality
service.句中t I dislike about tipping in the U.S.应该是定语从句,
sometimes the restaurant staff forget that tips are supposed to be a reward for quality
service做表语从句,那how是做什么的?