Lot's of lots of bad riot safety advice going around. Whatever else you do, don't use lemon juice to wash out tear gas.
Just use water. Lots of water. Please don't fuck around with eyes. There is no need to be fancy. Please for the love of God just use water.
Medical professionals who know their shit and want to use the proper sort of saline, ignore this. Don't go squirting random contact lens solution into random people's eyes. If you are a normal person and want to treat tear gas JUST USE WATER PLEASE
As a general rule, when you are in a combat situation and untrained, absolute simplicity is the safest thing. Water is simple. Everyone can flush a face with water. Please stick to this. Use water and a lot of it.