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Sewage treatment is an essential process in a more advanced society. Untreated sewage can reenter the water system and spread disease. Land around a sewage treatment plant would be cheap, as it is a less desirable area to live, because of the bad smell.

Down the sewers to the sewage treatment plant, just like when we flush the toilet or take a shower or brush our teeth or wash our hands.

In many cities runoff from the streets also goes into the same sewers, but as heavy rains can cause the sewage treatment plant to overflow and allow untreated sewage out, there is often a separate sewage system for this that does not go to the sewage treatment plant.

Sewage travels from your home by pipes. The flow is due to the slope of the pipes so the sewage is essentially flowing downhill to a collection well or pit.

The collected sewage is pumped from the pits into a forcemain which pressures the material to a sewage treatment plant.

In rural ares or industrial parks sewage sometimes flows to a collection tank which is pumped out and into a truck which carries it to sewage plant for discharge to the treatment system

Methanogens would likely live in a bog a sewage treatment plant or a cows intestine. They can only be seen with a microscope and not naked eyes.