I don’t know anything about plumbing. I can’t fix the leak in the sink myself.

I don’t know anything about plumbing as I can’t fix the leak in the sink myself.

I don’t know anything about plumbing, but I can’t fix the leak in the sink myself.

If I know something about plumbing, I can fix the leak in the sink myself.

I could fix the leak in the sink myself if I knew something about plumbing.