I am not sure exactly what you are asking, but I think you are wondering whether you could inject steam through your existing manifold. I suspect the heat might warp it, but even if it didn't, I think the slots on the manifold are too large to maintain any steam pressure, and all the steam would escape through the first few slits it encountered in the mash tun. You need something with smaller holes to restrict the outflow and maintain some pressure so that you get an even release of steam throughout the steam manifold. There are just too many large openings in a CPVC lauter manifold to do this, I would think.