Well, after cleaning everything with water and a rag or what have you – to remove all heavy debris and any visible gunk or residue…
Then you would fill the system with fresh clean water only, and add about 3 to 4 ml (about 2/3 to 3/4 tsp.) of it per gallon of water. You want to run this through the system for probably at least 4 hours. Make sure all your water pumps and air-stones are running, you want this mix to thoroughly get in every spot any of the water and microbes can get into.
And don’t forget to make another mix at the same strength to soak any misters, sprayers or feed devices/lines and any media you plan on reusing. And any tools, like measuring cups or syringes.
Also don’t forget your EC/TDS and pH meters, these need to be thoroughly cleaned as well. Refer to those items manufacture’s instructions on how to clean them.