Flowers briefly rinse, then the whole thing in a suitably large saucepan, which is covered. After 2 to 3 days, transfer the liquid into bottles (strain the flowers and lemons). The syrup can then be diluted with water (even mineral) in about 1:5. We have already used up the first batch (15 liters diluted). Most importantly, you will have wonderful elderberry fragrance in the kitchen for 3 days.
If flowers are left, dry them and make tea from them in the winter.