FOG, Sewer Litter and the Septic Tank
Down to the tank
The drain pipe from the house to the septic tank has a diameter of only 100mm, the same diameter as a margarine tub.
The pipe from the kitchen sink to the drain is only 40mm in diameter. The pipe from the toilet to the drain is only 80mm in diameter.
Putting FOG and "non-natural" objects into the drains is risky at all times.
Unlike houses on a sewerage system, the "non-natural" objects don't go far and they don't rot. The FOG goes onto the pipes and coats the walls of the tank. "Non-natural" objects you drop down the toilet are not destroyed in the tank. Those cotton bud sticks, and the panty liners, they'll still be there and recognisable when the tank is pumped out.
When good tanks go bad!
You put three kinds of things into the septic tank, along with a lot of water - organic material, inorganic material, and chemicals.
Organic material is what you do naturally in the toilet, and waste food from washing up. It could be other things, such as food scraps, but food scraps just fill the tank and cause it to be emptied more frequently. It is stuff that can rot.
Inorganic material is stuff like the plastic backing strips from panty liners, tampons, plastic bags, and the like. See Toilet and Shower Don'ts for details. It is stuff that cannot rot.
Chemicals are household and medical compounds that are designed to clean and/or kill germs. They are not "natural", whatever it says on the package, and should not be put into a tank which will let water out into the waterways. However, keeping your tank clean and your house dirty doesn't make sense, so you have to use them and then wash them away down the drain. Keeping the amount you use to the minimum makes sense.
"Natural" Chemicals
Everything in our physical universe, apart from energy (light, electricity, gravity, and magnetism), is chemical!
So-called "natural" chemicals are made directly from plants, but the chemicals they extract cannot be found freely flowing or lying on the ground in Nature. As soon as they are created in the factory they are no longer "natural" and are just as capable of damaging the environment as the chemicals which are brewed up from other sources. Be wary of all chemicals.
Chemical Warfare
The bacteria and fungi in the tank break down organic material into almost odourless gases which vent unnoticeably, and a sludge which is much more compact than the materials originally put in. The inorganic stuff stays as it is.
The chemicals however, may be "pro-active", and have a deadly effect on the bacteria. Some chemicals will react with and kill bacteria, working until all the chemical has found bacteria to react with. Bleach and disinfectant for example, and any medicines which kill bacteria, will all affect the good bacteria in the tank.
When you are cleaning your house you should never mix cleaning products to do a job, in case you create poison gas, or cause a chemical reaction that damages what you are cleaning or your skin. When you use more than one cleaning product, and wash each one down the drain, then they mix in the tank to create an evil brew. Products which are harmless to bacteria on their own can, when mixed with other "harmless" products, become bacteria killers.
When the bacteria are dead, the tank doesn't biodegrade the organic material, which just fills up the tank. The soak-away area becomes clogged, particularly with FOG. And the pong begins...
Choose Avoidance, not Cure
You can spend a lot of money on chemicals to keep your septic tank "healthy", but by changing your habits, and by using a Fat Trap to collect your FOG, you can avoid a large amount of trouble and expense. Avoidance is cheaper. The extra effort it requires is well worth it compared to the trouble that is created when the tank goes rank.