DEEP: System Design

System Design

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.

Portable Toilets

While a portable toilet is not technically considered a MSD under the law (since it is not "installed"), it may be the simplest, least expensive way to comply with the law.


  • Requires minimal space.
  • Low cost.
  • Simplicity.
  • Reliability.
  • Can be emptied via suction wand at a pumpout facility or at a dump station designed especially to receive portable toilet waste.
  • Can be emptied ashore if pumpout facility is not available.


  • Limited capacity

Holding Tank Systems

Holding tank systems vary in complexity depending on what they are designed to do. There are four basic arrangements.

1. Deck pumpout only.
The holding tank is installed in line between the toilet and the deck pumpout fitting.


  • 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: {[Illustration of how the deck pumpout system works.]}

  • External pump required to evacuate tank.

 System Design Continued

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Content Last Updated on October 3, 2019.