I guess by eaten they mean rotten - it’s warm down there. There are definitely no rats. In fact port environmental health inspect ships every 6 months for evidence of pests. There are no insects onboard apart from the odd few that migrate on with the crew. Bed bugs is everyone’s nightmare and usually swiftly dealt with. On deck when you are close to port you’ll get flies, but as the accommodation is air tight and positive pressure they rarely get in. It’s really odd when one does and really noticeable.
I’ve only ever visit a sub twice while on a sub support ship so never done a trip nor wanted to. Working ships don’t have a lot of windows so some trades don’t get a huge amount of sunlight either. Most workspaces are artificially lit. Engineers especially spend much of daylight hours down in the machinery spaces and can often be quite pale. Deck crew are out in it constantly and by comparison are weather beaten!
Flooding the toilet thing never happened. Toilets onboard are vacuum. When you flush the waste is sucked away with only a tiny amount of water (about a cup full). The holding tank is a biosphere (never use bleach to clean toilets the engineer will kill you and feed you to the biome) and is looked after very carefully to keep the tank “healthy”. If the biosphere is looked after well then the tank volume and smells are well controlled. The contents will be pumped out either alongside or to a waste collection ship (who take all the grey water (sullage) and oil slurry off too).
Subs can be maintained this way by support vessels at sea. Human waste, as with the macerated food waste and sullage can be pumped out into the sea. There are laws governing where and how this can be done.
There is an officer onboard who has responsibility for working out the water requirements of the ship. All the fuel for the ship must be sufficient for the journey along with domestic water and fire fighting fresh water. Then you need to balance the storage of all these (water, fuel, oil, sullage, bilge water/oil) and pump them across tanks to maintain stability. Water can be produced by processing sea water mostly using Reverse Osmosis. This is done by the engineers on instruction of the cargo officer. It’s all fascinating stuff. Submarines will have similar challenges but they don’t use diesel fuel as they are nuclear powered. I know that stability underwater is completely different to stability on the water and now I’m curious so I’m going to ask about that now 🤔