The RV / Marine antifreeze that I use is designed for potable water systems and winterizing swimming pools and it is completely non toxic. I use the walmart supertech brand which is $2.99 a gallon. The main ingredients are water, propylene glycol and glycerine which is what is used in vape juice and skin care products. It also acts as a corrosion inhibitor and since it already has water in it I use it at anywhere between 1/2 and 3\4 strength.