I use Nikwax Tech wash which is designed for activity clothing like this stuff. The reproofing spray by them though is designed for lightweight Outdoor gear, Gore-tex jackets and the like. Although it is good stuff, I don't think that it is good enough for biking gear. Reproof with something stronger as Chris suggests for real results.
I have Weiss gear too and have washed it successfully. Take out the thermal liner and the armour and wash the jacket in warm water in the bath or shower. Don't be too vigorous with scrubbing brushes and the like, but you can give if a good soak. Do use Tech wash or hand washing soap flakes, don't use fabric detergent or softeners because they can cause issues with the outer fabrics drawing in water afterwards. Don't wring it out, leave it to drip dry and reproof. Some proofers need wet fabric, some need dry. Check first before applying it. Hope that helps.
I realise that by listing this here, I have shattered any image of being a hard core biker that I have ever managed to accrue!
