An overhead projector, false teeth, bullets and animal offal are among some of the more unusual things found in the Western Bay of Plenty sewerage system as contractors deal with a "particularly bad" week for blockages.

In Tauranga city, 20 per cent of all wastewater overflows are caused by foreign objects being flushed down the loo. Congealed fat was responsible for a further 28 per cent of overflows.

Among unusual items found by Tauranga City Council contractors in the city's wastewater system was a deep fryer a few years ago, plus cellphones, underwear, glasses and children's toys.

Communications adviser Marcel Currin said the main problem with anything foreign getting into the wastewater system was blockages, "whether from fat build-up or rags, nappies and items of clothing".

Advertisement

"Rags get tangled in pump station machinery and can jam them up."

This week was considered particularly bad for blockages, with 10 reported to the council including a large accumulation of fat at an address in 17th Ave.

"The consequence of a blockage is that wastewater has nowhere to go and it bubbles out of the nearest manhole.

"Not all blockages lead to overflows, but they still require work to clear," Mr Currin said.

"Basic rule is if you didn't do it, don't flush it."

The city pipe network runs about 1200km with about 15,000 manholes and up to 154 pump stations.

In the Western Bay of Plenty, there are 62 wastewater stations, seven stormwater stations and about 540 grinder pump units in Maketu.

Utilities manager Kelvin Hill said the council experienced, on average, about 12 pump failures and perhaps two wastewater overflows a month.

"We've had a few unusual items over the years. Such items include an overhead projector in Te Puke, boxer shorts, bras and undies, bath towels, bed sheets, scissors, toy cars, false teeth, cell phones, knives, forks, spoons, money, rings, animal offal (the entire insides of a sheep blocked a pipe in Te Puke), newspaper, drink bottles, an asthma inhaler, tennis balls, golf balls, bullets, and syringe needles."

"Foreign objects can cause blockages which can lead to overflows and environmental pollution. They can block and damage sewer pumps, some items can also be dangerous to staff," Mr Hill said.

Of all the items listed, masses of congealed fat - known as fatbergs - were among the biggest issues.

Mr Hill said the council now routinely flushed certain lines in the district to prevent blockages "though we've never had anything like the seven tonne fatberg found in France a couple of years back".

In Rotorua, the unusual items discovered by local council contractors include a hedgehog, pig's head and blocks of punga.

Several items are forbidden to be flushed down a toilet.

These include dental floss, socks, rags, clothes, hygiene products, baby wipes, nappies, anything that has a lot of fibres in it, paint, thinners, oil, grease, petrol or diesel, glass, metal, gravel, sand, aquarium stones, seafood shells, plastic, cat litter, stormwater runoff, strong chemicals, wood, rock and concrete, plastic wrapping, cigarette butts, and condoms.