This is what I do with my white hoses.
Find someplace to run the hose downhill and cap the end.
Mix gallon of water with 2 tablespoons of PLAIN laundry bleach.
Funnel water and fill hose. Leave sit for an hour
Flush hose out
Re cap end.
Mix two tablespoons of vanilla. Genuine. Artificial does not work.
Fill the hose and leave sit overnight.
The vanilla does not leave a vanilla taste. It just absorbs other tastes, odors and smells. I haven't a clue as to why. This even works in a green hose.
The treatment lasts many months.
BUT!
Having the sun broil the hose raises Cain with the longevity of the treatment. I shade my hose as much as I can.