What I'd like to know is what are the two pipes, one large one small running from the toilet/shower cubical to a space with a screwed down fibreglass cover under the dinning table. It looks to me that this cover is glued as well as screwed down, so I thought I should find out what it's all about before I remove the cover.
Also does the water from the shower flow into the bilge and then pumped out from there.
Answer for the toilet
The larger is the inlet into the tank connecting the toilet to the tank.
The smaller pipe is a breather for the holding tank which is located under the table.
Not a good idea to tamper with the tank top.
The outlet pipe will be located coming out of the tank top covered on the way by a box cover vertical against the shower bulkhead front, leading to the deck fitting.
Answer for the shower
The shower water (grey water) runs into the bilge created for this water, then its pumped over the side. The pump is automatic and activated by a float switch in the bilge.