Are they the ones where the inside bit flaps out and there's an extra little booster that can go inside too? I'd soak the whole thing in that case cos most of the absorbant bit is attached to the outer. Then just wash it. Or you can soak it after the wash, don't think it makes much difference! I normally put a tiny bit of detergent in a bucket of water and do a quick handwash of it. You can leave it to soak for half an hour if you like, then rinse it thoroughly and then soak it in plain water for as long as you can, 12-24 hours is perfect. Then I do a final rinse in the machine and dry.