plastic Compost Bins
Probably the most common compost bins in use are the round black or green plastic bins that are readily sold in hardware shops or nurseries. They are common because they are relatively cheap to buy when compared to the cost of materials to construct a full sized three chambered timber compost bin and there is no work to set them up.  Simply place them in a corner of your garden and start filling. 

The main advantage of plastic compost bins is that they are easy to move around.  One compost management method is to place the bin in a part of your garden that needs compost added to it and once you have finished the composting process simply lift the bin off the compost and move it to a different part of the garden.  The finished compost mound that remains behind can be spread around the immediate area.  By doing this you reduce the amount of carting of compost that you have to do.
Photo of plastic Compost bin with side vents and the lid on upside.
Plastic Compost bin with side vents and the lid on upside with a brick on top of it to hold it down.
Close up photo of plastic compost bin.
Detail of the upside down lid showing the holes drilled into it to allow rainwater to flow into the compost bin.

While plastic compost bins offer an instant composting solution  they have two drawbacks.

Small size of plastic compost bins.
Plastic bins are usually smaller then any bin you will make yourself and, like all small compost bins, are likely to have greater fluctuations in temperature and moisture levels.  See Size of compost bins for more details.

Lack of ventilation.
The tapered shape of these bins (the top being smaller then the bottom) and the waterproof nature of plastic  means that there is less ventilation than bins made out of wood, straw or chicken wire provide. This can create a much wetter compost mixture, especially if you are adding a lot of household slops to the bin.  A compost mixture that is too wet will often have a putrid smell to it that attracts flies and is unlikely to produce good quality compost. 

If you have a plastic compost bin that does not have side vents on it than I suggest you consider drilling holes in the sides of the bin to allow some cross ventilation.  This will reduce the likelihood of the compost becoming too wet.

While plastic bins can give you compost that is too wet, because the lids of compost bins are usually watertight, the compost can also become too dry.  One way you can reduce the likely hood of this happening is to place the lid on upside down and drill some holes in it to allow rainwater to flow into the bin.  To keep the lid on place a brick on top of it.  If the compost mixture becomes too wet than simply place the lid on right way up for a while.