This has been covered quite extensively in
homebrew digest and
rec.crafts.brewing over the years.
If you are sensible about the use of sanitizers and your septic system is healthy, regularly pumped and properly sized, you will not have a problem rinsing your equipment or event dumping sanitizing buckets into a septic system.
A tank for a 3-4 bedroom house should be at least 800-1000 gallons or more, so a gallon of diluted sanitizer is further diluted by
three orders of magnitude when it hits the tank.
Remember that brewing sanitizing agents are not sterilizers, and not a substitute for cleaning. They are designed to eradicate only a certain portion of the microbial population on clean surfaces. You could not, for instance, kill a yeast cake in 90 seconds by filling a bucket with 9-12 ppm of iodophor. The biological portion of a septic system is quite like a yeast cake.
I personally think this is one place where the less-exotic sanitizers (
e.g. bleach and iodophors) have an advantage over the other chemicals because they so readily evaporate.
The greater concerns for brewing with septic tanks are usually not chemical.
- larger amounts of organic material - septics were meant to finish digesting pre-digested material, not lbs of grain and hop leaves
- hop oils - any oil is bad for septics
- large amounts of high-volume water - can saturate a lateral field, stir up sludge in tank.
- non-biodegradeable items- hop bags, fittings, and anything else that mistakenly goes down the drain is less of a problem on a sewer system than a septic.
A clothes washer is far more damaging because of the greater concentration and variety of chemicals (including dyes), combined with sluff-off of fabric from clothes.
Before anyone goes off and tries to re-plumb their brewing waste liquids away from their septic, check with your county health department. Chances are very good you will create an illegal open sewer and subject yourself to a hefty fine -- heftier than the cost of installing a septic system.
I found that just a little bit of change in practice can radically reduce your waste sanitizing liquids.
- Use shallow, wide containers instead of tall ones and lay tall or long items down instead of stand them up in a bucket
- Keep containers covered
- reuse sanitizing agent from one carboy into the next
- don't fill containers, close them up and roll them so the sanitizer has the appropriate contact time with all surfaces
- tailor your water chemistry so the sanitizing agent is more effective at lower concentrations (this generally means acidifying)