Automatic toilet bowl cleaners may take the form of discs of concentrated cleaner you drop into the tank which help keep the bowl sanitary for a few weeks to a couple of months or more. These may delay cleanings by hand, but they’re not meant to replace them completely. They also can’t clean and disinfect the outside of the bowl, seat and lid, places where plenty of germs accumulate.
Automatic cleaners containing bleach may be great at killing bacteria, but that may come at the expense of plumbing components inside the tank. Bleach is especially tough on rubber compounds, likely leading to shorter service life for parts such as water seals and gaskets and hastening the day when they’ll need to be replaced.
Liquid Bowl Cleaners
Liquid bowl cleaners made for scrubbing toilets by hand typically contain phosphoric acid or hydrochloric acid and perhaps a disinfectant. Phosphoric acid is the safer choice, but it doesn't work as quickly. Products containing hydrochloric acid “must be handled with great care as they can damage skin, fabrics, carpeting and metals,” says Don Aslett, author of The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros. “Never use bowl cleaners anywhere but the inside of a toilet bowl, and always (wear) rubber gloves and eye protection when you apply them.”
Brushes and Swabs
Brushes are good for cleaning out light residue every so often, and they will dislodge a surprising amount of bacteria by themselves. It’s time to replace a brush when bristles start to flatten out and spread away from the metal ring, which can permanently scratch the bowl if it’s rubbed hard enough against the surface. All-plastic brushes are available that avoid this problem.
For full cleaning and disinfecting, consider a toilet swab, which has strips of cloth, cotton or synthetic fabric mounted on the end of the cleaning handle. Unlike many brushes, swabs can push most of the water at the bottom of the bowl through the drain trap. Then, undiluted bowl cleaner applied to the bare bowl has the best chance of working well.
Additional reference:
Jeff Bredenberg, editor, Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine.