All solids that go down the drain [food, hair, grease, 'ground-up food', and sand used as laundry-soap filler] will collect somewhere. Either in the septic tank or else in the leechfield.
Septic tanks are easier to clean then leechfields.
It is nearly impossible to be so closely restricting the things that go down the drain, so as to avoid all solids.
If you eat meat, there will be fats that pass through you. At cool temps those fats become solids in the septic tank.
When you shower, oils from your skin get washed down the drain. At cool temps some of those 'oils' become fatty solids in the septic tank.
So between your toilet and your shower stall, many solids go down the drain to become effluent in the septic tank.
Some municipalities require all septic tanks to be pumped every 3 years. Other municipalities have no such requirement.
Some systems go for 20-years [and longer] without any problems.
I have seen systems marketed where an air-stone is placed in the bottom of the septic tank, and air is bubbled up through it. This changes the bacteria that thrive in the septic tank, so they can digest 99% of all solids [except for laundry-soap fillers] into liquids that can pass through your leechfield.
Adding an air-line like that might be a neat thing to consider.
When our tank was installed I added a 2" stand-pipe, so our tank could be pumped out without un-burying it.
Even if you desire to use a composting toilet or outhouse, you will need to first put in a septic-tank / leechfield [even if you never use it].
I have been told many times that once your septic-tank / leechfield are installed, then you may freely go on to using it or any other system you wish to use.
We were looking at some fairly expensive composting toilets at one time. Then that idea got put on a back-burner, as we had to install a septic-tank / leechfield. In the interval we discovered that there are some very inexpensive composting toilets that you can use.
We like composting toilets, as they take much of the burden away from the septic-tank / leechfield.
It is also common to see homes where the black-water and grey-water are separated. Black-water going to the septic-tank / leechfield; and grey-water simply going outside into the forest or garden. This idea also takes some of the work load off of the septic-tank / leechfield.