Unless you're in a location where you absolutely can't leach the liquid waste out into a leach field (like right on a lake), the tank usually just settles the solids and give the liquid some time to mingle with whatever biological processes are happening in the tank.
When the ground doesn't perk naturally, it's common up here to build a mound system where you have a mound of soil that does perk and vegetation (grass) on it to take up the liquid.
A fully closed tank is basically the last resort. We have friends with a house right on a lake, and their tank had to be pumped every three weeks before they had a kid. I can't imagine what the interval is now.
When the ground doesn't perk naturally, it's common up here to build a mound system where you have a mound of soil that does perk and vegetation (grass) on it to take up the liquid.
A fully closed tank is basically the last resort. We have friends with a house right on a lake, and their tank had to be pumped every three weeks before they had a kid. I can't imagine what the interval is now.