When you use the bathroom, some good bacteria comes out too. I suppose bad bacteria is ok in a septic too...not sure on that. Anyway, different bacterias break different things down. The bacteria expelled from our bodies helps to "eat up" solids. It helps the solids decompose to become liquids.
You know how a banana sits on the counter and starts to turn black, so of course your kids won't eat it, even though it is still good. So you forget about it in day to day things and pretty soon you pcik it up, due to fruit flies flying all around in your kitchen buggin you, and as you pick it up you notice that there a watery-ish brown liquid seeping out of it. This is its decomposing process.
A tank needs the enzymes/bacteria to decompose the things put into it. Garbage disposals (yes, we have one...you need a bigger tank if you are going to have one), toilets, washers with kids clothing in them (boys and their pockets)....all these things send stuff into the septic that needs to be broken down.
Oh, also, we have had issues with one lady in particular. Each septic is designed according to the number of bedrooms you have, if you have a garbage disposal, and if you have a large bathtub or not. This one lady uses only 40 gallons per week. Now, that sounds nice, but her septic is designed to have 400 gallons A DAY run through it. It does not matter that she lives along, she has a big house and there are sepcifications for house sizes, soil types, etc. For 3 yrs we had to go thaw her septic for her and each spring had to fix it because she refused to up her usage. Water flowing through the septic each day keeps it from freezing in the winter (out of a hundred septics, this is the only one we have ever had issues with) and keeps the bacteria hydrated (instead of drying and shriveling) so it can work. Her septic froze and clogged. It was under warrenty so my dh worked on it for free, until the county got involved. The county realized she was not using enough water and insisted that if she not use more water or follow the instructions of the installer (dh) then they must pay the county for an engineer to come and put special things in...bunch of foolishness it seemed...and we never heard from that lady again, nor did the county!
Septics are made to be used. They NEED that water flow. You can check into how much water usuage a day your septic is meant to have. If it is newly designed and installed the installer will know or the county will have record. HOWEVER, do not go to your county if you think you may be in need of a new spetic. You don't want that added expense until you have the $ for it.
Here we have POS inspections. EVERY house with a septic must have it inspected BEFORE it is sold. Some realtors make you do it before (the good ones do this) so you know what to expect (will the house needing a new septic effect the sale price?) and such. If you call an inspector to come and look (here an inspection is $250) and your system fails, the inspector BY LAW must inform the county. Otherwise he will lose his license. Also, there are different levels of compliance. I mentioned before the Imminent Public Health Threat. With that one, the spetic must be fixed within 10 days (fixed means a new one installed) or you have to move out until it is installed!
If you have a Non-Compliant system, there are different levels, the most frequent one is one where you have 2 yrs to install a new spetic. Very few comply with the new laws....
There are really neat septics out there too. There is one that is considered "experimental" that people on tiny lots on lakes can use. Most these tiny lots are too small for a septic. This one neat one is a tank (maybe a type of plastic? Not sure, we usually use concrete) that is filled with Peat Moss in a way that waste flows thorugh it. They say that the peat moss is a natural purifier and claim that you can DRINK the water that comes out! The demonstrations are REALLY slick! Our county is really slow at approving new things, so not too many have been used here, if any. We are a bit behind the other counties, but at the septic meets we see loads of neat stuff.