Hey I know this is a stupid question but I'm having really hard time figuring it out. What line connects to the fuel pressure regulator from the bottom? The engine is a H22A in a 3rd gen prelude. Thanks..

 

The return line to the tank. It'll be a hard line at the firewall (I assume), usually the largest one.

 

The fuel pump and filter feed one side of the fuel rail, the regulator is controlled by vacuum and is mounted to one end of the fuel rail. It evacuates the fuel rail of fuel (dependent on vacuum) and sends it back to the tank through the return line.