Most people say not to bother with the petcock on the radiator, as 90% of the time they will be stuck, and break when you put force on it.
Also, if you have the stock dexcool in there, there is a chance it will be thick and not drain properly from the small petcock hole. Everyone I've spoken to advises just dropping the lower rad hose, much bigger opening to get your potentially thickened coolant out.. more flow on the way out just seems more thorough to me. I know I've heard of people with actual chunks of dex and junk come out of the lower rad hose that would've just blocked up the petcock. The only real issue with that is the spring clamp which can sometimes be a real *****.
As for the bleed valve, it's on top of the tstat housing. Just follow the upper rad hose to where it meets with the block, that is where you will find the bleed valve. It's pointed out in the manual engine diagram if you have your manual.
I dont think you need sealant unless you develop leaks.. sometimes when you clean the coolant system, you wash away rust and junk that was blocking up holes that developed, and so you open up a leak.
And yeah, as stated you dont really need to mess with the knock sensors.
Just drain it with the lower rad hose, wash out the reservoir bottle, reconnect the hose and fill it back up with straight water, run it up to temp with the heat on... drain it again, then fill it with your flush solution if you're gunna do that and run it as per the directions. Maybe then fill and drain twice more with straight water to get all the cleaner and residue out. Get your 50/50 mixed up, maybe even slightly more coolant than water to make up for the water you already have left in your block that didnt drain. Then just bleed properly and call it done.. just open the bleed valve and fill it slowly to minimize air trapping... then I guess run it with the valve open until you see coolant start to run out and close it all up. Just keep an eye on the levels the next few days.
