I make laundry detergent with wood ash.
Once I’ve sieved the ask I put it in a bucket so it’s half full. Fill it to the top with water, preferably rain water. Give it a stir then leave it for a couple of days, stirring it everyday. There will be a clear liquid above the sludge which is what you want. Gently take this away and store it. You can add more water and repeat the process.
Add the sludge to the garden or compost.
When using I add a few drops of essential oil for a scent.