One important thing to remember about washing waterproofs with Nikwax is that
there must be no other soapy stuff around in the washing machine when you use the Nikwax, as the Nikwax doesn't work if it come into any contact with soap, which is why they always say on the container that you must at least do a complete wash cycle with no soap and no clothing in the machine to reduce the possibility/ likelihood of contamination. Failure to do this will indeed lead to the 'Nikwax is rubbish' sentiments - which I had until it was pointed out to me that ...
Following the Nikwax instructions made quite a difference ...