To let WD-40 work without dilution, turn off your toilet’s water supply, and flush it once to remove as much water as you can. Next, shake the can and directly spritz the stains.
Let it sit for a few minutes before scrubbing the stains in a circular motion with a toilet brush. You may need to do this a few times, particularly with older stains.
In addition to doing away with stains, WD-40 lubricates the inside of your toilet bowl, helping to prevent future stains from sticking to the bowl and seat.