This is how I water my giant Hoya pubicalyx cv. “Royal Hawaiian purple” and Hoya australis. The bottom leaves are getting in the way of my watering can, so I carry them into my bathroom and give them a cold shower, hitting as many leaves as I can in the process. Even though Hoya are succulents, they love water and high humidity. By watering the leaves as well as the soil, I prevent spider mites and aphids from infesting the plant. And as a bonus, I remove any soil, fertilizer stains and dust from the leaves as well.
After a good shower, the vines immediately start to grow much faster than they did before. At the moment I do this once a month.