Dorothy, biological detergents, mainly used in washing machines, contain enzymes which attack stains caused by grease, protein, fruit juice and starchy stuff. You can wash at slightly lower temperatures. The enzymes can upset the vital bacteria in the septic tank (which break down the organic matter). Non-biological detergents are what our forebears always used! They are always labelled "non-bio" in the UK as far as I know. Arguably, bleach is even worse for septic tanks. We have never obsessed over our septic tank but over 35 years we have routinely avoided bio detergents and used only minimal amounts of bleach. We tend to clean excessive grease from pans and plates with kitchen paper towels before washing up and we never flush non-degradable stuff down the toilet (wet wipes, cotton buds, tampons, etc.), never a problem for us but we have to "educate" visitors, which be a tad awkward! It doesn't take much to cause problems. Lots of baths, showers, washing up, machine washes and other domestic water use close together can slightly and temporarily overwhelm the system, and we get a slight whiff from the outflow occasionally when we have a houseful of family, but on the whole the system is very resilient. And we don't pay sewerage charges, which has saved us tens of thousands over the years. The whiff doesn't bother us as we have large pig and chicken farms close by, and when the wind is in the wrong direction...

As for the shorts, sandals and bare feet, it's thought that cellulitis (which is caused by bacteria that normally live on our skin in harmony) gain access via little cuts, scratches and insect bites to deeper layers of skin. Well I garden in shorts and sandals most of the time and I should think I get about a thousand nicks every summer, most of which I'm never even aware of, and I get bitten by horseflies dozens of times a day between June and August. As they itch for ten minutes (I'm blessed in that regard) I ignore them ((mozzies are a bit different, and if they're around I use a repellent). Somehow, from now on I can see myself being a bit more careful but not exactly changing the habits of a lifetime...