Is it ok to rinse buckets with tap water? Or even rinsing filters with tap water?

I do it all the time with my buckets. The tiny amount of tap water left over should not cause any issues. Rinsing filters with tap water will kill any beneficial bacteria on it. I would also be a little worried that the filter would "hold" a little more FW than desired. I can see this potentially being an issue if your water is chlorinated.

I agree. Buckets are certainly no problem, but yeah, anything with beneficial bacteria on/in it, or anything that will hold more thana little water, you may want to steer clear of tap.

Even if chlorinated, letting the buckets sit for a while, or drying them with paper towels and letting them sit, you should be good to go.

D

I rinse buckets, nets, and all that stuff with tap water. I give test equipment a final rinse with RO just to avoid contaminating the sample.

When you do a water change, the old water that you take out of your main tank can be used for cleaning filter media. You will maintain your beneficial bacteria this way. I have filter sponges on my powerheads and protein skimmer. I use the same water to clean them also. My 2 cents :)

Use a bucket of the old water for scrubbing rocks in if they have algae on them and then give them a good swishing in another to rinse off all of the algae you scrubbed off.