: i am installing a sink on an exterior wall with a window in front can i ad 90's and 45's to go thru roof can a vent stack have multiple angles?
Yes. Just make sure all parts of the piping slant down so that any water which gets into the pipe from any source can flow downhill and out the drain. If there are places in the piping which slant the wrong way, water could collect in them and prevent a free flow of air. If there is not a free flow of air, a partial vacuum could form, and that would hold water in the pipe the same way you can hold liquid in a straw when you are sipping through it.