Borax or Sodium Borate is a weapon that can be used against Leviathans. It was discovered by chance when Sheriff Jody Mills was scrubbing the floor of Bobby's cabin and spilt some which dripped down on Chet.
Since Borax is in almost every cleaning product, it can be easily found.
Usage
Leviathans burned by Borax.
It burns them worse than any acid or element Bobby tried on his captive Chet, apparently the only thing capable of inflicting any real pain to a Leviathan. While borax causes them extreme pain, it cannot kill them and is usually used as a prelude to decapitation, with the heads disposed of a good distance from the body or simply to escape while the Leviathan is in pain.
Borax hardly affects Dick, unlike the other Leviathans.
Dick Roman, the leader of the Leviathans, is more resistant to its effect than most other Leviathans and, while he is still affected by it, it barely slows him down.
During the Raid on Richard Roman Enterprises, Sam created a borax bomb to attack Dick and Victor while stealing the Leviathan Tablet. The bomb sent Victor to the ground writhing in agony while Dick was relatively unharmed. Victor eventually recovered from the effects but was subsequently eaten by Dick for his failure.