Red Cross unit secretary Marg Treseder said she was "absolutely horrified" to see analogue TVs, computer screens and a broken pram near the Red Cross bin in the McCrae Street carpark.

"It costs the Red Cross money to shift this stuff... for each trip to the tip," Ms Treseder said.

Salvation Army volunteer Karen Henery said the ratio of rubbish to usable donations was "horrendous" at the King Street op-shop.

"Some bags are absolutely disgusting... I know some people have opened them and it's people's refuse," she said.

Ms Henery said "not a lot" of the Christmas donations pile, which initially reached the shed's ceiling and out the garage door, would be sold in the shop.

"A lot is dirty, or torn," she said.

"Why give us something you wouldn't use yourself?

"It's got to be useable and clean."

St Vincent de Paul Society retail operations manager Michael Rawlinson said donation volumes during Christmas were up 75 per cent on previous years, but two-thirds of this would be unusable.

"The (St Vincent de Paul) centre is always looking for good quality donations of furniture and clothing," Mr Rawlinson said.

"We don't want to discourage donation.

"Unfortunately at this time of year we do tend to get items that are soiled or broken.

"Obviously damp (items) or household refuse and food items attract ants, which makes other items in the bins useless and worthless."

Mr Rawlinson said it was only a "small minority" that were dumping genuine rubbish into the donation bins.

"I don't know if it's laziness or a belief that we receive government funding," he said.

"We're responsible for the waste as much as anyone else in the community and we don't get free tip fees."

On what charities will accept, Mr Rawlinson urged people to consider whether or not they would donate the item to someone close to them.

"The rule of thumb is 'would you give it to your daughter or son, to use?'"

"If you wouldn't feel comfortable, don't donate it.

"Those in need have lost a bit of confidence and quality of life and we just want to give them the assistance they need," Mr Rawlinson said.

"We wouldn't give them items that are unsuitable."

Mr Rawlinson advised people to ask at charity stores or search charity store websites for a more comprehensive list of what items were accepted.