Hmm, dunno about those photos. Here's the URLs, they're marked public on Flickr...
Water pump and left side of water heater on Flickr - Photo Sharing!
Vent pipe coming up from black water tank (I think) on Flickr - Photo Sharing!
I replaced that whole section of floor without replicating the cut-out:
I cut off the bench and will be installing a regular toilet there with a standard 3" hole through the floor, and other holes for the vent stacks and so on.
As you can see in that photo, I also spliced all the electrical cables that went to the circuit breaker box and 12V
fuse panel and pulled them forward, as I plan on putting the battery, breaker panel & inverter/charger around the front of the street-side wheel-well. My plan is to be able to use that space at floor-level for storage, inside the corner cabinet, which previously held the water heater, pump, and lots of tangled pipes. I moved the city water inlet & fill inlet forward as well.