Hi! I am Derpmaaster, lvl 85 Bronze 4 Top main. I've been playing League since the beginning of season 9, so my experience is pretty young, so that I haven't seen tank Ekko. Because of this, I will be fine if you take my guide with a grain of salt. Anyway, as you would find if you looked me up on op.gg or similar websites, you would find that I enjoy late game mosnters such as Sion, Veigar, and Nasus. Around when I started playing Urgot (late season 9), I discovered Tilterella. And so, I began to use Sion as my pocket pick. This was fantastic for me, since I only played 2 champs. Urgot and Aatrox. So I've been playing him for some time now. I'm still not an expert though. So, once again, for the safety of your rank, take my guide with a grain of salt.

This is kind of a dumb question to be answering, since most of you here probably already know how this works, but I'm still going to cover it, because it's important. So this all works because of 2 major things. 1st of all. His W gives infinitely scaling maximum HP. The 2nd reason is that you take demolish. Demolish is a rune that, after a time spend near turrets, your next attack against that turret will deal bonus physical damage scaling off of your maximum HP. That is why you build so tanky. It maximizes your damage against turrets. Also, the reason it is called Inting Sion, is because you literally wait for the turret or a champion to kill you, and using the ridiculous attack speed your passive grants you, murder the tower more. That is also why Titanic Hydra is so essential to your kit. It is an auto attack reset that makes your next auto attack deal bonus damage scaling off of maximum HP.

At the beginning, unless your jg wants a leash, wait in the bush in front of the alcove. wait for the minions to get down to around 100 HP, and charge up your Q. By the time it is fully charged, they should be below 80 HP. If you hit the enemy laner, that's a nice little bonus but is not essential. When there is an opportunity to proc demolish, do it! Earlier on you will not be doing much at all, but slow and steady wins the race! trading is pretty straightforward. E a minion into them, and Q with them still slowed, centering the Q them.

You are good in Teamfights doing tank things (i.e. CC and unkillable), also doing decent damage, but when you can, splitpush opposite whatever sidelane is opposite whatever objective your team is setting up for. Like, split bot if your team is setting up for Baron, or vice versa. All you really need to know for splitpushing is that, if you are under a turret, and an enemy is attacking you, KEEP HITTING THE TURRET. If you are dead, you deal more damage to it anyway.
So, now you should be able to play Sion with some decency. I hope this has taught you something. Thank you and Goodbye.