This is the way I've settled on after 33 years of practice!
I'm addicted to this technique. I lay down in the bathtub with the hot water from the shower nozzle spraying on my groin while the tub slowly fills. I cover my belly with one washcloth (to catch my semen) and drape the other one over my limp cock. When I tug the cloth towards my chest it pulls my cock up onto my belly and the sensation of the cloth dragging over my cock feels like one long, sensuous lick. Meanwhile the warm water cascading down from the showerhead is tickling my tightening balls like a million fingers. Two or three slow drags and my cock is fully erect.
Then I change techniques: I wrap the washcloth over my cock with one corner draped over the underside of the head and the other draped down over my balls. When I put my feet on the edge of the tub and jerk off, the end on my cock feels like a caressing tongue, and the other end hangs between my legs and flicks my asshole with each stroke. The hot water falls like rain on my cock, belly, thighs and chest, stimulating my entire body erotically. I tweak my nipple with my free hand and soon I'm coming hard, moaning and rigid with orgasmic pleasure. Remember that the tub was filling? As I drift into the drowsiness of the afterglow, I also float away, literally, in a tub of hot bathwater. Ten minutes later I come to my senses as the water reaches the overflow, and I pull out the plug. As the water drains from the tub I lose the sensation of weightlessness, gradually, and when I finally come to rest on the tub bottom I arise and finish my shower. What a way to start the day!!