Using clematises on a tripod to hide the backflow valve isn't a good idea since they'd have to lift the tripod, thereby disturbing the clematis, in fall and spring. A Class 3 clematis, which gets cut to the earth in spring and very late fall might work but those clematises get huge and could easily obscure your new planting area.
It's the word "debris" that really bothers me. Every time I see this thread come up I want to chastise the one who said it to you.
This is a (class 3) Jackmanii clematis - you can see how big it gets.