This is going to sound a bit mad, but I was watching that programme 'Cleanaholics' and one of the people they featured used a bowl of water and her hand to clean the carpet. She just swept her wet bare hand across the carpet and collected the bits. Feeling a bit bored I tried this technique and my carpet that has never been washed and is about 5 years old looks like new. The only problem is that your hand gets a bit sore.