Napisan is the product peeps are talking about that is for Terry nappy sanitizing. (so somewhere there must be people not using disposables. Well done those chaps.)
I use it for washing all my gear, good for shorts too as it helps to stop fungal skin infections. Sunlight is very good too when there is some. The fungus and bacteria that grow in pits and groins have evolved for dark damp places. Therefore they are even more sensitive to UV than a lot of flora and fauna.
I have read that a small dose of white vinegar is good for eliminating the whiff. Maybe do a wash of your old tops with vinegar then rewash with Napisan. Should do a reasonable restoration job.