A neat little trick with toxic in blight town is this.
You know the dung pies the giant moss dudes drop? You can throw a few of them and it will make you toxic. However, the toxic from that is waaaaaaaaaaaaay less intense than the toxic the blow dart guys will give you and prevents them from giving you their own toxic. So when you go to that place with the six or so blow dart guys to get that firekeeper's soul, taking a few dung pies with you can be a huge help.