I have three pipes coming out of the unfinished basement.

First pipe is for a shower.

Second pipe is for the toilet.

Third pipe is the vent pipe.

Question is - can I run a sink drainage pipe down the vent pipe?

If you are referring to installing a sink on a different floor and then using the vent to drain it, then the answer is no, you may not. But if you're putting a sink into the basement itself, it should be no problem, provided it was roughed-in properly - in fact, there should be a stub-out for a sink coming out of the vent pipe about a foot-and-a-half above the floor.

Good luck!
Moishe
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