Most importantly it’s on a boat so it’s called a head.
The button on the bulk head by the circuit breakers is to flush the head. The key switch in the same location is the macerator pump. The through hull under the berth deck is the overboard drain for the macerator pump. The through hull under the cabin deck is the pickup for the head flush pump. The storage tank is also under the cabin deck.
Use the head (#1 or #2). Use the appropriate paper as required. With the through hull under the cabin deck open, press the flush button and watch it disappear.
When needed and able, open the through hull under the berth deck, place the key into the macerator pump switch (mine is a round single sided key) and turn to start the macerator pump. If you would like, you can open the cabin deck hatch, open the inspection plate on the holding tank and watch it disappear again. I suggest if there a lot of solids and paper you flush the holding tank a few times. Also the holding tank breath mints work to reduce odors.
Sent from my iPhone using Tapatalk