If an ageing plastic cistern has become an eyesore because of discolouration, or you want to change the colour to match your bathroom, don't let the fact that it's plastic hold you back. You may be used to painting wood or ceramics, but with a little preparation, you can give a new, durable coat of paint to a plastic cistern as easily as anything else around the house.
Wipe the cistern down with some white spirit to prepare the surface.
Thin the paint with a small quantity of white spirit, approximately one part spirit to 20 parts paint.
Paint the cistern just as you would anything else. You should use an oil or latex-based paint for this, not a water-based one. If you use a latex paint, make sure that you select one with a high-gloss finish since this is for use in a bathroom. You can also use an oil-based enamel paint, such as you would use on metal cabinets for example.
When using solvents, make sure to keep your work area well-ventilated.