Cleaning and Stain Removal - urine deposits in plastic buckets

We use a composting toilet system with urine separation. The urine goes into a tank with woodshavings. However we have a problem with some of the outdoor privies where the urine is collected in plastic buckets which develop a deposit and a stain on the inside which is hard to clean. I am using white vinegar mixed with bicarbonate of soda but it takes a bit of vigorous scrubbing to remove. Bleach works OK but we don't want to use it in this bush environment. Any suggestions for a non-toxic method?

Vinegar is cited as non-toxic and very effective for dissolving mineral deposits. To prevent build-up of mineral deposits from urine, more frequent cleaning of the plastic buckets will lessen buildup. Allow vinegar more time to dissolve mineral deposits and reduce need for so much scrubbing. Coating plastic bucket interior with mineral oil or cooking oil may minimize the amount of minerals that adhere to plastic and provide sheeting action.

-That's a good idea twelvepole! Because we are cleaning the buckets daily so can't do it more often than that. We tried leaving vinegar in the buckets for a day or so but they still need scrubbing quite hard -it's a big chore! I think the oil is the way to go. Years ago, we had some black plastic buckets made from recycled plastic and they had a slightly oily feel to them and nothing stuck to them. But, being black you couldn't see if they were properly cleaned or not, and anyway we can't seem to get them any more.

If you are cleaning daily and still have the buildup, I wonder if the interior of buckets are not slightly rough and contributing to adhesion of minerals. It might be helpful, too, to put some water in the buckets to help with dilution of urine and dispersion of minerals.

Paint the buckets black with a high quality paint that is designed for plastic.

http://homeparents.about.com/b/a/010510.htm

What's the purpose of painting them black, please?

Paint would make the surface of the plastic bucket slicker and easier to clean. I doubt that paint would hold up under these severe conditions.