Once it's filled, let the solution soak for 30 minutes. Leave your tub filled up and let the soap solution break down soap scum and grime.
[header] How to clean a cast iron tub [title] Soak the tub in warm water and dish soap for 30 minutes. [step] As your bathtub fills with warm water, add a couple of squirts of a mild dish washing liquid to it. Let the mixture bubble up and create suds.