manual says it's a "blowdown connection"? new horizon's install manual has a picture with a valve mounted on it, is it the drain for the boiler? lower right as you're looking at the back of the unit. I'm confused because the manual says to place a tee on the inlet to adapt a drain valve and makes no mention of this 1/2" pipe sticking out at the bottom. thanks for any info, I'm finally digging into this project.