Ryn, I think they suggest not to use Napisan at all.........

Two hourly changes should be fine I would try a strip wash, or even just a couple of washes on 60. Apparently you shouldn't use dishwashing liquid if you ahve a front loader? Also, maybe try washing every two days. That's what we normally do, but if I leave them longer than that for any reason, they REALLY stink LOL.