Learn Swedish: Ett underjordiskt rör leder till det nya avloppet. - An underground pipe leads to the new sewer.

It ends in -t to agree with the neuter noun it describes, ett rör (a pipe). The word itself is built from under (under) + jord (earth/ground) + the adjective suffix -isk.

Can leder till be used metaphorically, just like in English?

Yes, absolutely. While it describes a physical path here, you can also use leda till to talk about cause and effect, such as Det leder till problem (That leads to problems).

Let's review the end of the sentence: why do we say det nya avloppet?

This is the Swedish double definite structure. Because there is an adjective (nya) describing a specific, definite noun (avloppet), you need the separate definite article det, the definite adjective ending -a, and the definite noun suffix -et.

What is the literal translation of the compound word avloppet?

Avlopp is formed from av (off/away) and lopp (a run, course, or flow). Literally, it is the place where water "runs away", making it the standard word for a drain or sewer.