Swanns static Defense + DarkPylons make the entrances almost unbreakable for the enemy waves. If it gets messy, concentrated beam or the pulse cannon quickly cleans up any problems. if they are on cooldown, timestop and blackholes also work pretty well.
The VoidThrashers, ZenithStones and Reanimators can easily be sniped with the LaserDrill (manually targeting) as long as you have vision. DTs and ShadowGuard also work pretty good.
I didn't need a single tank with Swann, the turrets and manually focusing the LaserDrill and its abilities were more than enough.