had a similar problem a couple of years ago, turned up to a job and loked at the carpet, I had no idea the carpet was white, her old man had used a crate of vanish mouse that I gathered had fallen of a back of a lorry and sprayed the whole lot then with a yard brush, brushed away, the results were apparantly amazing for about a week,
I cleaned with nothing but plain water then rinsed with a acid rinse, but wow dont know whats in the stuff but it came up like new, but foam took me ages, a light sprinkle of de foam crystals on the carpet and a hand full down the vac hose every now and then worked fine
James