On Mon, 30 Jan 2017 04:17:41 -0000 (UTC), Martim Ribeiro
wrote:

I've had a septic system for 15 years and never had it pumped out.
Yet I see neighbors pumping theirs every 3 years.

All I put down mine is crap and TP and pee (sorry for being blunt).

1. Pee just drains away.
2. Crap (I assume) dissolves itself (bacteria) over time.
3. But what about the TP?

Does the TP dissolve like the crap dissolves?
Or does the TP eventually fill the tank up?

(Why doesn't mine fill up then?)

It dissolves eventually, brand dependent. Some are worse than others.
Charmin (and similar) is supposed to be the worst.