There are two main types of wc's used on boats and each can be divided in two again. It has not been permissable for many years now on most navigations to use a toilet that pumps untreated waste overboard from what is known as a 'sea-loo'.

PUMP-OUT TOILETS

• Dump through - the seat / bowl is directly over the tank and the waste drops into it. These are again divided into 2 mains groups, the fresh water flush and the re-circulating flush. The fresh water flush uses water from the boats plumbing system to rinse/flush the boal. The re-circulating loo uses the liquid in the tank to rinse/flush the bowl (when the tank is emptied upto 10 gallons of clean water is added with the bloo to start off the process).
• Remote tanks - the waste is pumped, sucked (uses less flush water) or blown to a remote tank - the tank can be any where in the boat to use spare space - but it is best if the tank is balanced across the centre line so that it doesn't affect the trim as it fills up.

CASSETTE TOILETS

• Free-standing holding tank & seat - the rinse water is held in the'seat/bowl' fitting.
• Built-in seat with removeable cassette - fixed toilet from which a self-sealing holding tank is extracted.

COMPOSTING TOILETS

• The dimensions (33in x 25in) make retro fitting very difficult.
• Waste breaks down without use of synthetic chemicals or any additives.
• Uses power (claimed to be 0.6A) to run a fan as part of the composting process

TOILET TYPE

ADVANTAGES

DIS-ADVANTAGES

• Simple.
• Ceramic bowl.
• The rinse water is part of the boat plumbing.
• Hands free emptying - often done by someone else.

• Air displaced from the tank when the waste drops in may cause a smell.
• Winter ice/ maintenance can prevent boat reaching a pump-out station.
• Tank never clean - often left a long time between emptying.
• The size of the tank varies - may be small.
• Have to empty immediately when full.
• Cost of pump-out £12 to15 - 2 tanks, 2 charges. Expense can be greatly reduced by acquiring a self pump-out kit.

• No back smells.
• Ceramic bowl.
• The rinse water is part of the boat plumbing.
• Hands free emptying - often done by someone else.

• Complex machinery - sensitive to what goes down there! - easily blocked.
• Winter ice/ maintenance can prevent boat reaching a pump-out station.
• Tank never clean - often left a long time between emptying.
• May use a lot of water with the flush
• The size of the tank varies - may be small.
• Have to empty immediately when full.
• Cost of pump-out £12 to £15 - 2 tanks, 2 charges. Expense can be greatly reduced by acquiring a self pump-out kit.

• Simple.
• Normally no cost to empty - when cruising you usually pass an elsan disposal daily.
• When you empty it, it is relatively clean - you can easily empty it every time you leave the boat.
• You can carry a cassette in the winter but not a boat.
• If you have a spare cassette, you can empty the full one at your convenience. (Ha Ha)

• A full cassette may be heavy for you to carry.
• Air displaced from the tank when the waste drops in may cause a smell, although never as much as a dump-thro tank.
• The rinse water tank has to filled.
• Looks campingish.
• The seat level may be low.
• Plastic bowl.

Cassette

(Fitted)

• Same as the free-standing cassette

But also:

• The unit looks more like a household loo.
• The seat level is at a good height.
• The unit is very stable.
• The rinse water maybe part of the boat plumbing.

• A full cassette may be heavy for you to carry.
• Air displaced from the tank when the waste drops in may cause a smell, although never as much as a dump-thro tank.
• Plastic bowl.

• No back smells.
  
• Ceramic bowl.
  
• Normally no cost to empty - when cruising you usually pass an elsan disposal daily.
  
• When you empty it, it is relatively clean - you can easily empty it every time you leave the boat.
  
• You can carry a cassette in the winter but not a boat.
  
• If you have a spare cassette, you can empty the full one at your convenience.
  
• The rinse water is part of the boat plumbing.

• Complex machinery - very sensitive to what goes down there! - easily blocked.
  
• Cassette size 14L
  
• A full cassette may be heavy for you to carry.
  

An proven concept on land fairly new to boats.

• Uses no hazardous or environmentally damaging chemicals.
• A single user reported 18 months before needing to empty.
• Does not require special disposal - compost will produce wonderful tomatoes etc!

• Unit by Envirolet requires an area of 33in x 25in and installation of a vertical breather pipe
• 12v model has an extractor fan using a min 0.3A max 0.6A - but a lot less than a 12v fridge
• Sometimes a heater is required to assist the composting process
• Not enough boats have been fitted with these for an accurate assessment of possible disadvantages to be made

Paul's thoughts: My own preference as a liveaboard is the Thetford cassette system (or any porta potti system). There is no cost; in frozen conditions you can still carry a cassette but a boat will be stuck; with a spare cassette you have time to empty a full cassette; it is quicker to empty a cassette than it is to organise a pump-out; the cassette is relatively clean when it has been emptied; a cassette can be emptied out of working hours; as a weekender when you leave your boat you can do so with a clean/empty cassette everytime.