Backflushing sends water and detergent backwards through your grouphead, cleaning out coffee oil buildup. It's easy to do once you get the hang of it.
To keep your espresso tasting as clean and delicious as possible, we recommend backflushing your machine after every 20-40 shots or so. For most people this is once a month.
Find backflushing tools at Clive Coffee: clivecoffee.com/category/espresso_cleaning.html