In Mike's drawing I believe the grey tank is left and the black tank is right. Remove your basement wall and follow the sewer pipe down to confirm.
And as mentioned above you will need to pull down the section of coroplast under the basement.
Put a pry bar under the washers and a 1/4" socket on a drill. Run the drill in reverse and pry down to get the nails out.
When putting it back up re use the washers and use 1" #12 self tapping bolts/screws. You have to push up really hard but the screws will go through the nail holes.
Here's a good video of lubricating valves.
Valve lubrication making lube holes for silicon grease