cleaning guinea pigs

Hello, I was wondering if I needed to groom my guinea pigs. They are American short hairs and I have never groomed them before, but they do shed a lot on the fleece. If I were to groom them, would it be okay to use a clean, unused tooth brush to do it, or would I need to get a special brush? I...

Does anybody know anything about something called a grease gland? it always kind of been on my guinea pig and I never knew what it was. I have to sort it out but I'm confused :) He also HATES baths and water? haha x -thanks