I have an older faucet in my tub, it is a single pull and turn model. Clear plastic knob. It groans when shut off and leaks water. I've been told that the cartridge might need replaced. I am not sure how to get it out. I've pulled the knob which allows me access to a brass looking cartridge that looks like it's held in place by a clip. How do you get the clip out.

We need a brand name before we can help. Sounds like a Moen but could be a Delta. Let me know, Tom

I believe it's a moen. There are no names on it.

Clicking on;http://www.moen.com/consumersupport/installation/moen0133/moen0133.cfm
Will get you to a installation guide for replacing a Moen cartridge. You can get a new cartridge from Moen for free call them at 800-289-6636,
Good luck, Tom