A properly functioning toilet should not emit foul-smelling gases. If your toilet smells like a sewer, take the following measures to get rid of the smells.
Avoid Excess Water in the Toilet
Sewer odors reaching the toilet can come from several different places. For example, it is even possible for odors from the septic system, if you use one, to back up to the toilet. Therefore, minimizing the production of foul odors in the septic system is one way of preventing your toilet from smelling. A good way of doing this is not to dispose of excess water into the toilet; doing that will saturate the septic tank and affect the treatment process, leading to overproduction of odors.
A clogged toilet also smells. The smelling occurs because the debris responsible for the clogging starts to rot within the pipes before they can reach the septic tank; some of the odor from the debris then flows back to the toilet. Therefore, prevent your toilet from clogging by not disposing of anything that is not meant for toilet disposal, such as plastic materials, down the toilet. If clogging does occur, use an auger, plunger, or drain chemicals to get rid of the problem.
Use Baking Soda
You can also use baking soda to combat foul smells in your toilet. Baking soda works because it absorbs gases and cleans the drainage channel; for the latter solution, you should also add vinegar to the mix. Pouring a cup of baking soda down the drain say, once a week, will work wonders for your toilet smells—assuming there is nothing else wrong with the toilet.
The toilet has to produce some smell because, after all, it handles waste materials. However, these wastes do not normally reach your home because they are trapped in the toilet and drainage pipe system. This means anything that interferes with the seals can lead to a smelly toilet because it will let the gases escape. Therefore, ensure that the seal around the toilet is always intact to prevent such odors.
Ensure the P-Trap is Functional
The P-trap should remain moist at all times if it is to perform its main function, which is to trap gases and prevent them from fouling your bathroom air. Several things can cause the P-trap to dry out; for example, it may dry out if it is damaged and leaking or if the toilet hasn't been used for some time. If this is the problem, diagnose the cause of the dry out and fix it so that the trap can continue trapping the foul gases.
The tips above should help prevent foul odors from your toilet; consult a plumber like Drainman The if they don't seem to help.