cat vomits white foamy clear substance

For the last 2 days my cat has been vomiting clear white foamy vomit. He cries out loud before he vomits. I put him outside to vomit. I have been giving him barefoots dewormer. I give him 2 droppers full for a (1 cup) bowl of water. i give him prill water like I drink. He drinks it up. The barefoot dewormer is for humans but you can give it to pets. It kills parasites and it tase great. I figure if I have parasites so does he. He is an out/in door cat, around 8 years old. He stays indoors most of the time. I was thinking about using my zapper on him. My zapper has wrist bands I could put on his legs. I did this the other night and he hissed at me. It doesn't hurt because I do it and I used the lowest frequency on him. I could put him in his carrier to zap him. I also was going to buy some paralixer for him I learned on the CZ cats can't taste this. Tweet