How to Flush a Marine Toilet

Written by meghan k. cleary
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On board a ship, marine toilets are to as "the head." Marine toilets are made in manual or electric vacuum flush styles. On most pleasure boats, the head flushes to a holding tank, which has to be pumped out when full. Many boats also have a "Y-valve," which when flipped bypasses the holding tank for direct overboard discharge. It is only legal to discharge sewage overboard when more than 3 miles offshore, so before flushing your marine head make sure that the Y-valve is directed towards the holding tank.

Skill level:

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Things you need

  • Manual or vacuum-flush marine head
  • Marine-grade toilet paper
  • Air freshener

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  1. 1

    Before using the toilet, turn the handle to "Wet" and pump a small amount of water into the bowl.

  2. 2

    After using the toilet, add ample water to rinse the bowl and lines. (Note: Some manual toilets have a foot pump that draws saltwater in, rather than a "Wet" setting.)

  3. 3

    Turn the handle to the "Dry" setting or use the manual handle to pump the bowl empty. Remember to close the through-hull after using the head to prevent seawater from flowing back through the lines and filling the head while the boat is in motion.

Tips and warnings

  • It is difficult to avoid the unpleasant smell associated with marine toilets, which comes from organic matter dying in the saltwater hoses. Most boaters keep a bottle of air freshener to spritz after flushing, but using a generous amount of water (or switching to fresh water from the sink) when you flush will also cut down on the smell.
  • Unlike household toilets, marine heads are delicate machines. The best practice is not to flush any solids "that you didn't eat" through a marine head--this includes toilet paper, feminine products, hair from hairbrushes, etc. If you don't like disposing of toilet paper in a separate garbage can, it is wise to invest in marine-grade toilet paper that is very thin and quick to disintegrate.

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