Stop flushing wipes, fat and other waste down Helensburgh toilets, campaigners have pleaded.
The recent burst pipe at the bottom of John Street has brought the problem literally to the surface as infrastructure struggles to cope.
As well as waste that shouldn't go down the drain, there may also be movement of sub soil under pipes and cables thanks to rain and upsurging tides.
The burst pipe was installed in the 1970s but campaigners warned that there are many more Victorian-era pipes that will need attention far before this stretch is replaced again.
"We have all this infrastructure that's getting pretty shaky," said Angela Anderson, of Plastic Free Helensburgh, at the town's community council meeting on July 25.
The 400mm-wide pipe running along the seafront through the pumping stations to the treatment works at Ardmore split and caused a sinkhole at the start of John Muir Way in March this year.
East Clyde Street at Maitland Street was closed for investigation in May as well, Scottish Water confirmed.
Ms Anderson said the break at the bottom of John Street was eight metres long in the 400mm pipe, and she put the blame on what the public were putting down their toilets. She said both the burst pipe and pumping station were full of wipes.
She also said there was a problem with homeowners paving spaces in front of homes or using plastic grass which forces water to run off and add to the pressure on drainage.
Ms Anderson said it was "really important we try to save" grass verges.
"There are dozens and dozens of gullies on the roads that are grassed over and flooding," she added. "The council are relying on people reporting that there's a problem."
Ms Anderson praised Scottish Water and their contractors for repairing the recent split.
With the sewer network strained by rubbish dumped down the drains, there is additional pressure with extreme weather events such as the significant rainfall last October that saw flooding across Helensburgh and Lomond.
Scottish Water reminded of the "three p's - pee, poo and (toilet) paper" as the only items that should be flushed down the toilet.
A Scottish Water spokesperson said: “We are investing many millions of pounds across our network to meet the challenges we face due to ageing assets, increasing demand and climate change.
“Customers also have an important part to play by not flushing inappropriate materials such as wet wipes and nappies down the toilet.
“We are committed to working with stakeholders and communities in Helensburgh to protect the environment.”
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