This is not the Bitcoin Mixer, but you are close…

Bitcoin Mixer is a Tor Hidden Service that allows you to mix bitcoins with other users to make the bitcoins anonymous. To access the Bitcoin Mixer site you must use Tor.

Recommended is to use the Tor Browser Bundle or Tails and then go to
http://grams7yngnpr5rzf.onion

As bitcoin is not anonymous without a bitcoin mixing service, anyone can see the flow of bitcoins from address to address on the public block chain. To break this chain you need to use a bitcoin mixer or also called a bitcoin laundry. Bitcoin Mixer is a bitcoin mixing service set up to help people stay anonymous, it’s used to mix your bitcoins with other users to break the track to the bitcoins original source. Bitcoin Mixer will receive your bitcoins on one wallet and then send bitcoins from another wallet to a address you specify.

http://grams7yngnpr5rzf.onion

grams7yngnpr5rzf.onion