2 tbsp of betadine per gallon may be easier. They call it Povidone-iodine (PVP-I), also known as iodopovidone.
From the wikipedia on the net:
"Following the discovery of iodine by Bernard Courtois in 1811, it has been broadly used for the prevention and treatment of skin infections, as well as the treatment of wounds. Iodine has been recognized as an effective broad-spectrum bactericide, and is also effective against yeasts, molds, fungi, viruses, and protozoans. Drawbacks to its use in the form of aqueous solutions include irritation at the site of application, toxicity, and the staining of surrounding tissues. These deficiencies were overcome by the discovery and use of PVP-I, in which the iodine is carried in a complexed form and the concentration of free iodine is very low. The product thus serves as an iodophor.
Diluted iodophor is often used by brewers and winemakers to sanitize equipment and bottles. Its major advantage over other sanitizers is that when used in proper proportions, it does not require rinsing. However, it can leave unattractive orange-brown stains on plastic parts and equipment if left in contact with them.
It is often supplied in different concentrations and is further diluted with water before use. The label will advise the appropriate dilution ratio, commonly 1:1000 or 1:100. Equipment to be sanitized should be thoroughly clean and left in contact with the solution for at least 2 minutes.
Diluted iodophor is used extensively in the dairy industry.
Iodophors are most effective in an acidic medium (pH 2 to pH 5) but are effective up to pH 7.
It is inactivated by proteins if the pH rises above 4 and is inactivated if the temperature rises above 50°C, as the iodine is driven off as a gas.
The optimum concentration is >200 mg/l free iodine with a contact time of 2 minutes and 100 mg/l free iodine for cleaned and dried equipment. In a nonfood-contact application the concentration may rise to 500 – 800 mg/l.
"Based on a review of the available toxicology data, the [US EPA] has concluded that iodine and iodophor complexes are of very low toxicity by the oral, dermal, and inhalation routes of exposure.""