Dave taught me...
First, place the tip of your tongue along the gum line behind your front teeth as if you were about to pronounce the letter L. Then, while keeping your tongue firmly in place, blow a constant stream of air out of the two sides of your tongue, it's a sort of Thl sound. I never could master the village just up the road though.
And this place is a bit of a nightmare too
Machynlleth. ( We just referred to it as the home of those blooming nationalist........)