City West Water managing director Anne Barker said while the bulk of the community was responsible about what it disposed of into sewers, there had been several recent instances where blockages occurred as a result of inappropriate disposal.

"Our response crews sometimes respond to incidents where waste has been inappropriately disposed of in the sewerage system," she said.

"These types of incidents can be costly to repair, can risk the safety of our maintenance staff, and also result in public health and environmental hazards if the sewers become blocked and overflow." Ms Barker said items which should not be put into the sewerage system included cooking fats, unwanted chemicals, hygiene items, food scraps, unused medicines, solvents and engine oils.

Businesses are also advised to ensure that they comply with their trade waste agreement when discharging trade waste to sewer.

"There's no excuse for placing oil and chemical wastes in the sewer - these sorts of contaminants can have a serious impact on the environment, and most councils offer a free disposal service for these."

Ms Barker said householders who disposed of used cooking fats down kitchen sinks ran the risk of costly repairs caused by blockages to the drains within their properties.

"It's a basic principle of science - water and oil don't mix and if you rinse oils and fats down your drains, over time, there's a chance householders will be up for an expensive plumbing bill to unblock their household drains.

"The sewerage system is not a rubbish bin, so food waste, personal hygiene items, oils and chemicals should be disposed of in other, more environmentally friendly ways."

Ms Barker said contaminants in the sewerage system could have a direct impact on treatment processes and it was everyone's responsibility to keep the sewer system free of them.

"What goes in your toilet, and down your sinks and drains, can affect the environment and even though sewage is treated, many household substances and items that get into sewage can still end up in Port Phillip Bay and the ocean."

What you shouldn't flush:

■Food scraps.

■Cooking oils and fats.

■Cotton buds.

■Cigarette butts.

■Unused pharmaceuticals.

■Condom s or sanitary products.

■Plastic bags.

■Engine oils, petrol, diesel, kerosene.

■Chemicals, paints and pesticides.