A huge mound of wet wipes blocking a drain took workers several hours to clear to prevent a sewage leak.
Welsh Water has written to customers connected to the pipe in Abertillery, Blaenau Gwent, following the recent blockage.
It has urged all members of the public not to put wipes down the toilet adding some are "wrongly" labelled flushable.
Water industry body Water UK found unflushable wipes made up around 93% of the material causing sewer blockages.
Imogen Brown, Welsh Water's head of wastewater networks, said a single wet wipe is enough to cause a blockage but workers filled four bin bags.
"While the majority of people do the right thing and dispose of wipes in the bin, there are still some that are unknowingly risking their family homes," she added.
"This incident in Abertillery is a stark reminder that only the three 'Ps' should be going into your toilet - pee, poo and (toilet) paper - and everything else should either be recycled, if your local council provides this service, or put in your bin."
Customers have also been advised not to pour turkey fat, gravy and other leftovers down the plughole at Christmas - as they can cause fat, oil and grease to build up in the sewer, blocking it.