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SESK: Stuff Everyone Should Know · sesk.info/boat-msd-type-iii-holding-tank

On a boat with a toilet, which kind of marine sanitation device is a holding tank?

Type III; Types I and II treat and flow through.

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  1. Type I
  2. Type II
  3. Type III ✔

Why: Boats with installed toilets must have a working marine sanitation device (MSD). Types I and II are flow-through devices that treat sewage; Type III is a holding tank that's pumped out on shore.

Huh, didn't know that: Boats over 65 feet must use a Type II or Type III MSD.

The dad joke
Why does the holding tank never gossip? It keeps everything to itself.
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References

Answer: Type III. Boats with installed toilets must have a working marine sanitation device (MSD). Types I and II are flow-through devices that treat sewage; Type III is a holding tank that's pumped out on shore.

  1. A Boater's Guide to the Federal Requirements for Recreational Boats (USCG) www.uscgboating.org/assets/1/AssetManager/Boaters-Guide-to-Federal-Requirements-for-Receational-Boats-20231108.pdf
    Type I and Type II are “flow-through” devices, while a Type III is a holding tank.
    Checked 2026-10-09.

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