Three systems cover almost every narrowboat. A cassette toilet uses a small removable tank that lifts out through a hatch and empties at an Elsan disposal point found at most marinas and many canalside services, the most common setup on smaller and older boats. A pump-out toilet flushes into a larger fixed holding tank, emptied less often via a pump-out point, usually for a fee. A composting toilet separates liquid from solid waste, needs no chemicals, and is emptied less frequently again, appealing to boaters minimising both cost and environmental impact. Which one suits a boat depends on tank size, mooring pattern and how often you're near an emptying point: worth weighing up alongside the rest of what it costs to run a narrowboat. The plumbing changes from boat to boat; the name on the side doesn't, see our first year afloat gifts.
The tank is a fact of living aboard that nobody raises at the boat show. Where it ends up, and what the bathroom loses to it in a seven-foot beam, is the subject of narrowboat interiors.
Choosing between the three systems.
A weekend boater who is back at a marina every few days manages happily with a cassette. A couple living aboard and cruising for weeks between services may prefer a fixed tank, because the extra capacity buys more time between stops. A composting toilet suits someone who dislikes the logistics of both, but it brings habits of its own: liquid and solids are kept apart, a dry bulking material such as coir or sawdust goes in after each use, and the solids still have to be disposed of legally, so check the local arrangements before committing. Count the people aboard as well as the tank size.
Mistakes that cost a weekend.
The commonest is leaving the emptying until the gauge is nearly full, then finding the next disposal point is closed, out of order or a long day's cruise away. Check the route for disposal or pump-out points before setting off, and treat the half-full mark as the cue to plan. Use only the paper and fluids the system is designed for, because the wrong products can block a pump, and never empty waste into the canal itself, which is not permitted. When viewing a boat to buy, ask where the tank sits, how it is emptied, when it was last cleaned and how the pipework runs. The guide to life on a narrowboat shows how chores like this fit into an ordinary week afloat.