For over 2 years we used a home grown method of keeping our holding
tanks clean & odor free. I bolded "holding" because that's what they are designed for - they are not septic tanks. Any off the shelf chemicals targeted at the RV industry that claim to break down waste are typically a gimmick and cost money that would be better spent elsewhere. A septic system breaks down waste and sometimes needs enzymes added to enhance its process. Its important to distinguish between a holding tank and a septic tank when reading the rest of this post.
We recently found an excellent article written by Charles Bruni that detailed a process similar to ours where he goes into great detail of how the system/process works.
With his permission we converted the article into an Adobe Acrobat .pdf file for download.
I know that this will strike a cord with some readers due to its use of chorine but you need to remember that if it was harmful to septic systems and the environment then municipalities wouldn't add it to our drinking water.