We recommend using Ecover spray cleaner, or equivalent, and a brush. If you need something more abrasive, gardeners lime seems to work well for other customers. Toilet paper varieties make no difference, ethically it might be preferable to go for a recycled brand. It is important to avoid using large amounts of water as this will simply be added to the liquids already in the system waiting to be evaporated.
See attached file for Do's and Don'ts poster than you can print and hang inside the loo.