Oh, I thought you meant the sewer.
Yeah, follow that. Then go through the factory and you'll find yourself in a room with Mr Mimes. Run through that, fight a trainer, than you'll end up in a room with a Magneton and a few Hypno. Head straight up and avoid the confuse rays, and there will be two stairs. Go through the one that isn't blocked and you'll find a Pinsir.
Sig and Avy by Me ~