Grease Trap and Grease Interceptor Odor Remedies Why Does My Grease Trap Smell? The grease trap or grease interceptor's bad odor does not necessarily indicate that the device is full. The smell of traps and interceptors is often due to four primary reasons; lack of service, broken seals, faulty plumbing, and vent pipe. Try pinpointing the odor source to prevent costly remedies by doing your...