My landlord keeps ignoring my plumbing issues, what do I do?

I moved into a house 4 months ago. It is a one bathroom, with a washer hook up, and a 40 gallon water heater. Within a week, I noticed these problems: the kitchen sink and washer drain into the bathtub and toilet, causing overflows and a ridiculous amount of scum. I also only get 5 gallons of hot water at a time. I have mentioned this to her a total of 6 times, both face to face and in emails. She always says that she'll get to it, that her handyman will call me within 48 hours, etc...so far nothing has happened. What should I do if she keeps ignoring me?