When shooting underground, having a good lighting setup is key.
For drains i usually shoot at f8 with an exposure of 10-15 secs, iso around 200. Check your photo to see if there's no burnt out whites and adjust your settings if necessary. A tripod is a must, as is a pretty wide lens.
Use multiple lights that you place around in the room or tunnel that you're photographing. I have diffusers om my lights that give a soft even light and avoid spots in your picture.
Another thing you can do is put a person in your picture for scale. You can backlight that person and/or have him/her hold a light source.
Here I have placed a bright spotlight in the right tunnel. I, behind the camera am holding a diffused light to give detail to the foreground and the person in the picture is holding a flashlight with diffuser.
Here I placed a spotlight to backlight the person and a diffuse light to give some detail to the foreground.
Just play around with shadows, different setups and camera settings. This type of photography is very hard and challenging, but can be very rewarding.