A sewer-like smell around a toilet can come from too little water in the trap, a failed seal at the base, poor venting, or a wider drain problem. Where and when the odor appears helps separate those causes.
Check the bowl water first
The visible bowl water forms the seal that blocks drain gases. If the level falls over hours or days, look for cracks, siphoning when other fixtures drain, or simple evaporation in a rarely used bathroom.
Odor at the base points toward the seal
If the smell is strongest where the toilet meets the floor, especially if the bowl rocks or moisture appears, the seal may have failed. Stop using the toilet if water is leaking around the base.
Gurgling changes the diagnosis
If the toilet gurgles or its water level changes when another fixture drains, a venting problem or shared blockage may be involved. That is different from an odor limited to the porcelain or floor seal.
Odor from several drains needs broader diagnosis
When several drains or bathrooms smell at the same time, cleaning one toilet rarely solves the cause. Check rarely used traps and look for main-drain symptoms before arranging plumbing service.