my cannon i455 ink jet printer will not print in black, only colour?

I have soaked the printhead in cartridge flush & cleaned it. I have replaced the ink tanks twice. I have deep cleaned twice using the maintenence programme. I can only diagnose a full waste ink tank from the help disc. Where is it? & How do you empty the waste ink tank?!! It is little used & only two years old, is this a realistic lifespan for a printer!! Any help appreciated before I cannibalize it to see these infamous waste tanks!! Thanks Charlotte.