PREVIOUS | TOC
| NEXT
Where it is intended to install a Sewage Holding Tank System in a Pleasure Craft, the
following guidelines (reproduced courtesy of ABYC) are recommended to be followed.
Additional provincial and local design requirements may apply. |
A3.0 |
Sewage Holding Tank Systems (Voluntary) |
What Are Some System Design Alternatives?
First, we’ll look at some of the advantages and disadvantages of portable toilets and holding tanks in general.
Later, we’ll examine holding tank systems and their plumbing arrangements in greater detail.
Advantages
Requires minimal space
Low cost
Simplicity
Reliability
Can be emptied via suction wand at a pump-out facility
Can be emptied ashore if pump-out facility is not available
Disadvantages
Limited capacity
A3.3 |
Holding Tank Systems ^ |
Holding Tank Systems vary in complexity depending on what they are designed to do. There are four basic
arrangements.
1. Deck Pump out Only
The holding tank is installed in line between the toilet and the deck pump-out fitting.
Advantages
Allows use of existing toilet
Sewage goes directly into the tank
Simple to install
Minimal equipment requirements
Does not require a through hull for discharge
Disadvantages
External pump required to evacuate tank
Figure A3-1 Deck Pump Out Only |
![Figure A3-1 Deck Pump Out Only](/web/20060212064306im_/https://www.tc.gc.ca/marinesafety/TP/TP1332/images/Fig-A3-1.gif)
2. Overboard Discharge Option After the Holding Tank
A diverter “Y” valve is installed in the line between the holding tank and deck pump-out fitting to allow the
tank’s contents to be pumped overboard. The “Y” valve must be secured to prevent overboard accidental
discharge.
Advantages
All sewage is pumped into the holding tank.
Vessels will use pump-out facility in port.
Disadvantages
None
Note: A “Y” valve is not required in this option. The deck pump-out fitting and the overboard through-hull
valve are normally pressure tight and will function alternatively as selected. Use of a “Y” valve, however, will keep unused sections
of the hose or pipe from being unnecessarily “wet” (filled with sewage) and provide an
additional safeguard against accidental overboard discharge.
Figure A3–2 Overboard Discharge After Holding Tank |
![Figure A3–2 Overboard Discharge After Holding Tank](/web/20060212064306im_/https://www.tc.gc.ca/marinesafety/TP/TP1332/images/Fig-A3-2.gif)
3. Overboard Discharge Options Both Before and After the Holding Tank
“Y” valves are installed in line between the toilet and holding tank and between the holding tank and deck
pump-out fitting.
Advantages
Flexibility in discharge options. “Y” valves must be secured to prevent accidental discharge of untreated
sewage.
Disadvantages
Flexibility is offset by complexity
Figure A3–3 Overboard Discharge Before and After Holding Tank |
![Figure A3–3 Overboard Discharge Before and After Holding Tank](/web/20060212064306im_/https://www.tc.gc.ca/marinesafety/TP/TP1332/images/Fig-A3-3.gif)
4. Overboard Discharge Option Before the Holding Tank
You should install a holding tank for use when boating in environmentally sensitive areas or when moored
or dockside. A “Y” valve is installed in line between the treatment system and holding tank.
Advantages
If a Type I or II treatment system is installed between the toilet and the “Y” valve, treated sewage can be
pumped directly overboard, unless the vessels is in “No Discharge” waters
Disadvantages
“Y” valve must be secured to prevent accidental illegal discharge
External pump is required to empty holding tank
Figure A3–4 Overboard Discharge Before Holding Tank |
![Figure A3–4 Overboard Discharge Before Holding Tank](/web/20060212064306im_/https://www.tc.gc.ca/marinesafety/TP/TP1332/images/Fig-A3-4.gif)
These four basic arrangements can be adapted depending on the number and type of toilets installed and whether
inline waste treatment is desired.
PREVIOUS | TOC | NEXT
|