This recipe assumes that you already have a sourdough starter and it is made with whole wheat flour. If using a white flour starter you will probably be fine if you reduce the hydration a little, and of course the final loaves will not be 100% whole wheat but near enough.
This is a link to one description of making a starter, but you will find many more on the internet.
https://www.eatingwell.com/recipe/265890/whole-wheat-sourdough-starter/
Once you have an active starter you don't need to discard anymore, I keep about 500g of starter in the fridge and use what I need to bake, when I am down to around 50-100g remaining I feed my starter to bring it back to 500g let it start to ferment again and once you see it is getting active return to the fridge until you need it for your next bake. I keep an 80% hydration whole wheat starter (80g water/100gFlour) but this works for 100% hydration as well. Others just keep 20-50g of dormant starter in the fridge and take it out and feed it the day before they are going to bake, this is commonly known as the scrapings method.
https://www.youtube.com/watch?v=Uj6YpNCUYYQ
To make 2 900g Sandwich loaves