According to UKClimbing Nikwax wash in stuff is the thing. However it didn’t work that well for me. However I need to give it another go. As they say in their reviews you shouldn’t leave your jacket too long before cleaning and re proofing it.
Nikwax Tech Wash and Tx-Direct are what I used, along with others, but they don't work. Grangers Fabsil used to work....up until you try using the garment, then it rubs off after a couple of hours. Which is what I and others have said on the thread I linked.
Cycling, only my jackets need waterproofed, the rest of me I let get wet, or sometimes I wear waterproof overtrousers.
My jackets are various versions of the
Altura Night Vision range.
For 15 years I have been using the above products, imo they work well.
Mind, I always wash by hand, rinse well, then wash in the Tx-Direct, then drip dry.
Not a big hardship, because I wash my commuting jacket only every few months unless it needs re-proofing.