Fast and fun, but watch out for trees and fences. About halfway down on a LH bend is a 6m waterfall with a shallow landing.
Takeout at the road bridge at the confluence with the Dringarth river (just north of Ystradfellte). To reach the putin head north up a steep hill, then take a small turnoff down to the river just after entering the woods.
Rainchasers is best experienced as an app.