Tasman District Council engineers are baffled that clothing and underwear are being flushed down toilets in Māpua.
The recurring problem has resulted in clothing blocking sewage pumps in the small coastal settlement.
Community infrastructure waters and wastes manager Mike Schruer said the clothing was causing problems at the Aranui-Higgs Rd wastewater pump station catchment.
Since the beginning of August, there have been eight pump blockages caused by t-shirts, singlets and underpants.
It is a problem that has occurred several times in Māpua over the last few years.
Schruer said the blockages take several hours to clear and are costly as the pumps must be craned out, pulled apart, cleared, reassembled and reinstalled.
Each blockage incurred a cost to ratepayers.
New sewage pumps were installed during a major upgrade of the Māpuainfrastructure last month and Schruer said there are concerns the clothing blockages could permanently damage them.
Engineers know the area the garments are coming from but cannot pinpoint the exact property.
Schruer said if residents suspected it was a member of their family, to please speak to them and point out the problem they were causing.
Anyone concerned it was a neighbour, could contact one of the Tasman District Council's wastewater engineers in confidence.
"In the meantime, please remember the sewage system is for wastewater only, clothes and rags should be disposed of by other means."