If your dog eats something toxic, you can administer hydrogen peroxide 3% solution, dosage = 1ml per lb of the dog's body weight (e.g. 20lb dog gets 20ml peroxide), with a max amount not to exceed 45ml (e.g. 45lb dog gets 45ml, 100lb dog gets 45ml) to force them to vomit up the toxin. Also, it needs to be done within two hours of the incident. If it has been longer than 2 hours, take the dog to the emergency vet. Anyway, the peroxide should induce vomiting within 15 minutes or so, and the vomiting may last up to 45 minutes. This should only be done in emergencies and when there are no readily available professional resources (e.g. vet clinic). Otherwise you need to take the dog to the vet.
Another note:
You should NOT administer peroxide if the dog is;
-already vomiting
-severely lethargic
-comatose
-has decreased swallowing ability
-has difficulty breathing
-is having seizures or other hyperactive activity
-has had recent abdominal surgery or megaesophagus (enlargement of the esophagus)
-consumed corrosive agents, sharp objects, or drugs
https://www.akc.org/expert-advice/health/how-to-make-a-dog-throw-up/
Key points:
Administer 1ml of 3% peroxide per lb of dog, not to exceed 45ml
Administer within 2 hours of incident. If it has been longer than 2 hours, take dog to vet
Don't administer if dog has swallowed something corrosive, sharp, or drugs, or if the dog has had recent abdominal surgery and/or enlarged esophagus