Yes they come in the kit. Only really for initial purging of air. The solar filling pump removes the rest.
A drain back requires an aav ( ideally solar rated) to be placed internally, need to be at the highest point iirc.
I personally wouldn't touch a drain back system, they are noisy and I'd imagine they would wear pumps alot quicker, the hp's are good, because when they overheat, the phials apparently pull away from the manifold to stop heating it.