https://success.ada.org/~/media/CPS/Files/COVID/Conducting_Respirator_Fit_Tests_And_Seal_Checks.pdf suggests a few ways to do proper smell tests.
The one with saccharin which leaves a sweet taste in your mouth without seal seems to be the easiest to do at home.
I personally did some testing with cider vinegar and found that a FFT3 mask reduces the smell when properly fitted.
https://success.ada.org/~/media/CPS/Files/COVID/Conducting_Respirator_Fit_Tests_And_Seal_Checks.pdf suggests a few ways to do proper smell tests.
The one with saccharin which leaves a sweet taste in your mouth without seal seems to be the easiest to do at home.
I personally did some testing with cider vinegar and found that a FFT3 mask reduces the smell when properly fitted.