installing petcocks

After losing power the other night, I went ahead and drained the block, manifolds, and heater core to be safe. Only takes a few minutes, but it would be easier with petcocks on the block. I have only have two drain plugs but the issue is that one of them has the knock sensor. I assume there is no way to put a petcock there. Does anyone have a solution for this. Also, It is kind of a pain to remove the heater hose to blow the water out, could you hook up a flush kit type setup and use it to blow out the core?

For the heater, cut the hose and install a barb on each end and a shut off valve in between. All the parts are available at home depot. Then you should just be able to unhook and blow out from there. This also helps should the heater ever spring a leak.