There will be dozens of ways to go. Some will say do nothing and take a chance some will not want to take any chances. I go with no chances so I look to what experts do to clean up /sterile things. They use chlorine like found in bleach to clean the water we use so that is good enough for me.
When I buy a used tank, I have no idea what the history may be so I go for a bleach soak on all the equipment. In a tank under 20-30 gallons, I fill it set the filter on and then add any décor like rocks or wood. Then a bit of bleach without scents or colors, just the cheap stuff? Maybe a couple tablespoons to half cup but it isn't a precise number as we don't know how much organic (dirt?) it has to clean but we just want enough. I let it all run overnight or so to make sure it soaks into everything and then drain and rinse. At that point it is diluted to almost the same as the tap water and just go as normal from there. If you are soaking gravel, I may spread it out and let it dry really well if I'm planning to store it. Wet/damp gravel can grow fungus and weird stuff so I want it totally dry first.
I like my plates clean before I eat and do the same for my fish, whether there is something bad there or not.