Wow... this thread is all over the ball park with questions.
To the OP... you will get MANY, MANY different opinions about whether to add antifreeze after blowing out the lines with compressed air.
The decision is heavily dependent on your climate.
If you experience only a few nights/ weeks of sub-freezing temps, then you likely can get away without antifreeze. If you live where it gets below freezing for months, then I would certainly consider adding antifreeze.
I also do both... blow out and add antifreeze.
For the few minutes it takes, it is good insurance against something happening.
It only takes a small droplet of water trapped in a faucet cartridge or plumbing valve to create a problem that you will find come spring when you pressurize the system.
To the other questions (which should have really been asked in a separate thread)
An air plug is readily available that screws into the city water supply that you can connect to, to blow out the plumbing system with compressed air. Many folks also make their own. I did.
For the black tank... usually not much problems here as it should be drained and any residual liquid can easily expand when frozen without hurting anything. I always let a cupful or so of antifreeze run into the P-traps and then into black and grey tanks (from the toilet or faucets) when winterizing.
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