To clean any of the foam pads and anything that comes into contact with the water, I would use water taken out of your tank. It helps maintain the Good Bacteria on everything.
Your be surprised how much will live in your fluval. I have pods
living in it! I was surprised at first to see things move around the bio-rings, but they are there!
So nothing but tank water for sponges, bio-rings, and other filtration media.
Like Airgoose2222 said, the pads will keep unwanted debris without breaking them down. This is why it is important to clean your filter at least once a month! The issue with Nitrates is because people don't clean the filters our enough.
I DO use regular tap water to clean all the plastic parts. I use Hot water and than I dry it off with a paper towel. I leave all the filter media in the bucket submerged in old tank water. So only canister filter itself is cleaned out with the normal tap water. The plastic holding the Rings I leave in the Tank Water, but I can clean all the other plastic parts!