What are purifications breathing?
controlled breathing and visualization
you breathe in to a count, visualizing cleansing energy saturating your body with the breathing in, the breathing out, again to a count, visualizing your body being emptied of its waste and pollution
different versions, differing in the details abound, here is one I found by doing a google search:
9-ROUND BREATHING
This is a pre-tantric purification practice in which you visualise the main 3 energy channels in the body. It is used in the beginning of a meditation session (after the prayers of refuge etc.) to calm and clear the mind in only a minute or so.
Make your breath somewhat longer and deeper, but don't exaggerate, if possible one should not hear the breathing. If you have a cold and one or both nostrils are clogged, just imagine breathing through the different nostrils.
Visualise the body as being completely empty and transparent, then inside it appears the Central Channel.
The Central Channel starts between the eyebrows, continues back just under the skull, and from the crown of the head it goes straight down to the level of four finger-widths under the navel, it stays a little in front of the spine. It is like a transparent blue tube, about the thickness of a thick drinking straw.
To the left and to the right are two side-channels, both transparent and the thickness of only a drinking-straw. The right channel is red, the left is white.
The three channels are flexible and just below the navel they connect with each other.
During the first round of breathing, INHALE through the LEFT nostril, keeping the right nostril closed with a finger. We imagine the air going from the left nostril into the left channel, up near the crown and way down to under the navel. There, the left channel is connected to the right channel, and we BREATHE OUT through the RIGHT CHANNEL by closing the left nostril with the same finger. Imagine breathing in pure white light, and when exhaling, imagine that all DESIRE AND ATTACHMENT which pollutes the left channel collects at the navel and leaves via the right channel as black smoke. The black smoke disappears beyond the universe. Repeat this 3 times.
Then the next round we INHALE white light via the RIGHT nostril, and all ANGER AND HATRED which pollutes the right channel collects below the navel and is EXHALED via the LEFT channel as black smoke. Again, do this 3 times.
The third round we INHALE white light via the LEFT AND RIGHT channel together and imagine them both being connected to the central channel below the navel. This CENTRAL CHANNEL is polluted by IGNORANCE AND CONFUSION which is breathed out as black smoke. Imagine that you BREATHE OUT via the POINT BETWEEN the EYEBROWS.
Normally do this not more than 2 or 3 rounds. 
