UK households are being advised not to pour cooking grease or coffee grounds down the drain, as doing so can lead to blockages and costly damage.
Why grease and coffee grounds cause blockages
When cooking grease is poured down the drain, it cools, solidifies, and coats the inside of the pipes. This coating traps food particles and can form stubborn clogs or large sewer blockages known as fatbergs. Once grease coats the pipe walls, coffee grounds, rice, and food scraps stick to it, gradually reducing water flow.
Blockages can result in slow drains, foul odours, backed-up wastewater in the home, or expensive repairs. Even washing grease down with hot water or dish soap does not prevent it from cooling and sticking to pipe walls further along the system.
Impact of coffee grounds on plumbing
Pouring coffee grounds down the sink is also a major cause of severe pipe blockages, plumbing damage, and septic system failures. Unlike water or soluble powders, coffee grounds remain solid and absorb moisture. They pack tightly in U-bends and pipe joints, trapping grease, soap residue, and food scraps to create dense, hard-to-clear blockages.
Grounds can also accumulate inside septic tanks and leach fields, disrupting pH balance, taking up capacity, and requiring expensive pumping.
Expert guidance on prevention
Although some online discussions suggest that coarse grounds help scrub pipes or that small amounts are fine with boiling water, most plumbing experts warn that the risk of clogs outweighs any benefit.
Plumbing website Wolseley explains in its guidance: "Outside drains do many important jobs, handling everything from domestic waste to leaves and outdoor debris. This means that they can become easily blocked but luckily drain unblocking is quite simple to do by yourself if a problem occurs. The best way of preventing your drains from blocking is by controlling what goes down them."
Wolseley adds: "If your drains connect to the inside of your home, you should make sure that no one is putting cooking grease or coffee grounds directly down the drains, as these are common causes of blockages. You can also add grates and filters to your outside drains to stop garden debris from blocking them. These are very effective against leaves, which can contribute significantly to blockages."
The guidance also suggests: "You can also add small filters to your plugholes indoors to catch food waste and hair from being flushed down and contributing to blockages. If your drains regularly block despite precautions, you may wish to start putting baking soda, vinegar, or small amounts of a chemical drain cleaner down your drains to help keep them clear for longer."
