Plumbing a Sailing Catamaran

The Head (Toilet)

"Yacht toilet? Sani-Loo or holding tank?"

"Where do I start?"

The thoughts of smell, sewerage and blockages soon come to mind and no matter how many ideas you come up with to exclude one from maintaining "The Loo", the fact is that you are going to get your hands dirty some day.

The thoughts here were simple, get the widest base which in the long run will improve stability and securing to the floor when compared to the smaller bases and some of the stories floating around.

Secondly, get the whole lot automated. In today’s world, these systems have been well designed and improved on and are now very reliable.

For the extra few dollars, this also provides that little bit extra padding (so to speak) and keeps the law on our side.

In summary, waste is sent directly overboard, or via a selector to the holding tank.

We have chosen this way for:

  1. Simplistic installation,
  2. KISS (Keep it simple Sailor) right up our ally, and
  3. Compliance with the new State Sewerage Treatment Regulations.

Aft Saltwater Inlet

We have chosen to place a single saltwater inlet for the toilet under the shower floor, where access is easy and other 'wet area' components are stationed.

From there, the saltwater goes through a Marelon Seacock (ball valve) to a tee, one side to the toilet and the other to the deckwash.

We have had tremendous trouble here as no one seems to make a 'skin-fitting+90 degree elbow' (in bronze) that will hug the floor. They all protrude some distance from the skin fitting making the area required very deep.

We have chosen to use high pressure PVC pipe in this area as the floor area will be glued and screwed and we can't afford to pull this up in the event of a plastic pipe replacement.

The only access here will be via the ' shower access door ', a simple piece of resined ply.

Being below waterline, this section of the hull has been glassed as its going to get wet from the shower waste, saltwater inlet maintenance and a point for the removable speed-transducer.

This area was also prewired to allow the insertion of our first automatic bilge. Its job being two-fold, to remove shower ater and act as an emergency bilge, whether on the yacht or while away.


Treated Waste

With the ever strengthening regulations in Australia and in an effort to maintain the pristine areas that we wish to sail, we needed to stay abreast of the law or face the legal consequences that could force us to sell.

Using this as our benchmark, we drew a line-in-the-sand and we have to work forward from here. This is our slant on the treatment of sewerage from our vessel and not that of the designer, maritime services or any other legal body.

Also, sewerage discussed here is classed as waste from our toilet and not gray waste from the vanity or galley.

Our main cruising ground is expected to be the Australian east coast and for the uninitiated, this contains an ever growing labyrinth of sewerage discharge regulations, mainly no-discharge zones.

Outside these zones, boat harbours or marinas, or certain distances from an aquaculture facility, you may discharge or pump out untreated sewage.

All toilets have to be fitted with a macerator to help speed up the breakdown process, and this is now law in Queensland, Australia.

Added to this are three grades of treatment, A (best grade) to C (the least favourable grade).

These are discussed in more detail through the Queensland Government: Home, Environment, Sewerage site. We have chosen to go with Grade C, which at time of writing meant:

In Smooth Waters, no discharge within 926 metres (0.5 of a nautical mile) of any of the following:
a) a person in the water
b) aquaculture fisheries resources
c) a reef.

Would strongly suggest a good read of your States own requirements.

"get the whole lot automated. In today’s world, these systems have been well designed and improved on and are now very reliable"

Sketch of Toilet connections

Simple, yet functional. Finding the correct plumbing fittings to marry all the components became the challenge.


Drawing of Water System

One pressure pump, serving all freshwater outlets, hot water system and filtered water.


Freshwater Overview

Our catamaran water system carries three types of water - saltwater, freshwater (drinkable) and freshwater (non-drinkable).

The saltwater outlets include:

  1. The toilet (in the vanity area),
  2. Deck-wash (in the vanity area), and
  3. Desalinator (forward starboard hull).

Freshwater outlets include:

  1. The shower (in vanity area),
  2. Outside shower (starboard aft hull),
  3. Vanity wash basin (non-drinkable), and
  4. Galley sinks (drinkable and non-drinkable).

A Sailing Catamaran Building Project has more expanded information on this topic with many more photos.

The freshwater system is made up of three basic sections:
> Desalinator
> Freshwater drinkable
> Freshwater non-drinkable

The Desalinator is covered in its own section and will not be discussed here.

There are two tanks (one of 200L and a second of 150L) that provide the freshwater needs for the yacht. Based on our planned water use (again discussed in the Desalinator section), this size should prove suitable.

The tanks are the collapsible type and can be individually filled and emptied via their own shut-off valves. These components are stationed under the main sitting area in the saloon.

To provide water pressure to the whole system, we have chosen to use a pump with an accumulator. All these components are located in the vanity area under the sink.

We have purposely done this for two reasons:
> Easy maintenance access, and
> Single ‘wet area’ on the yacht.

Given that we will be proactive in the maintenance, easy access is a must and the pump units must be easy to work on. This however does have its own drawbacks in that additional plumbing and forward planning is needed.

Freshwater Pressurisation

Freshwater from the tanks are piped to this area with the pump purposely being positioned lower than tank level, making pumping more effective. Its here too that the system is pressurised.

Together with an accumulator, the on/off cycling of the main pump is reduced and a more constant system pressure exists.

The pump chosen is a common unit to allow for cheaper spares and replacement. We will also carry a spare pump which may seem over the top, but provide immediate replacement in the event of a malfunction.

It too is needed for the desalinator auto-flush-function (when we are away from the yacht), making its serviceability rather important in our case.

In the vanity area, pressurised water goes two ways:

Back to the ‘water tank area’, which supplies:
> The Galley, and
> Auto-flush of the Desalinator.

To the Vanity, which supplies:
> Vanity basin,
> External shower (cold only), and
> Hot Water system.

Vanity and Hot Water System (HWS)
The yacht has a single tap for the shower. The main reason for this is that we want to control the water use.

This control in turn reduces water waste (by those who use their big toe trying to find a suitable temperature before jumping in at start-up), reduces plumbing costs and also provides a single temperature for all showers.

The control and mixing is preset by ourselves, closer to the Hot Water system. Cold pressurised water is sent to the HWS where it is heated and then returned.

At the exit from the HWS tank, we have a mixer valve that reintroduces cold water and its here that we control the temperature. This warm water then goes to the vanity and shower.

An additional separate cold water line is run to the vanity sink.

Galley & Auto-Flush

The second pressurised return line (that runs back to the ‘tank area’) is split two ways:
> One line to the Galley, and
> The Auto-flush desalinator system.

A 'flick master' has been placed in the galley to provide this filtered fresh water through a filter on one side (even although the water should be clean from the desalinator) and standard freshwater on the other.

The amount of vessel use, specifically the periods and type of sailing we intend doing, will mean that freshwater will be sitting in the freshwater tank for extended periods between uses and while every effort will be made to 'turn-over' the water being used, one cannot guarantee that water made 12 months ago has been all used.

The last thing we want is to be buckled-over with gut aches caused by bacteria in the freshwater system three or four hours into a weekend away.

This outlet will have its own tap and the filters will be down to 1 micron. To keep the filter systems full, a one-way valve will be placed in the line below the filter too.

The auto-flush desalinator plumbing provides for flushing of the desalinator membranes each four days. There is more on this topic in the desalinator section.


There are two saltwater inlets on the yacht:
> Desalinator (forward starboard hull) and
> Toilet/Deckwash.

The desalinator inlet is covered in the desalinator section.

The toilet/deckwash inlet detail is listed in the toilet section, from where we continue.

Again, this pump is located in the vanity area above the freshwater pump. This is for the same reasons mentioned about the freshwater pump.

There are two filters in this system given that the water could be contaminated with plant matter. The deckwash has only one outlet (above the shower area) and a hose pipe is used to wash the entire yacht.