2 Pack 54mm Espresso Backflush Cleaning Disc For Breville Espresso Machines - 54mm Backflush Disc Compatible with Breville BES870XL/ BES878BSS/ BES880/ BES840XL/ BES810BSS

In a pinch, I've gotten away with wrapping the dual wall (pressurized) single shot basket with a couple layers of cling wrap. Just make sure the top is smooth so it seals to the gasket. It will do a back flush fine. But yes you will want to either buy a cleaning disk or blank basket for long term use. Here's a one on Amazon: https://www.amazon.com/dp/B0BYCXSVZD