carry water for (someone)
1. To serve, assist, or perform menial or difficult tasks for some person, group, or organization. Internships are a great way to gain practical work experience, but you'll be the one carrying water for the company while you're there. Immigrant workers are most often the ones who carry water for farm owners and construction firms.
2. To support a person, organization, or cause that one would not in reality endorse, as due to pressure, force, or pragmatic reasons. Once elected to congress, I soon realized that you must carry water for many groups that run contrary to your own personal politics. Though I personally found him repugnant, I carried water for him for two years because I thought it would open up many career opportunities.