Bathroom odors coming from toilet-to-floor gasket seal?

I'd replace the undersink air valve. If it's never been replaced, it's well beyond it's 'sell by'date! An '02s greywater tank is going to stink just about as bad as the black. Plenty of greasy dishwashing goop stuck to the inside of the tank over the years reeking. The 'worse on windy day' comment really makes me suspect the air valve. After 15 years, the soft rubber seal is bound to be cracked/wrinkled/stiff.