ESSENTIAL KIT - Holding Tanks                           (Black & Grey Water)

ESSENTIAL KIT - Holding Tanks (Black & Grey Water)

Black water from sea toilets should not be pumped (dumped) overboard unless the yacht is well offshore. Different countries have different rules.  Generally in tidal waters 4 miles offshore is the norm. In non-tidal waters like the Med it is 12 miles although almost no-one follows that rule unless they are actually on passage.

Obviously don't ever pump out in anchorages, no-one likes to swim in dissolved poo.

Grey water from showers and sinks is potentially even more harmful to the local flora & fauna as it coats the bottom with a sludge that kills everything off.  Ideally grey water should also be captured in the holding tanks but, in practice, very few yachts can accommodate holding tanks that are large enough to capture all waste water, grey & black.

In Turkey, authorities are increasingly providing pump out facilities at Marinas and Public quays.  Some free, most for a small charge and other private facilities quite expensive.  Once you get used to the process they are easy to locate and use and they certainly have improved the local water quality.  There are a number of marinas throughout Europe that offer pump-out,  I expect more will appear before too long.

You need to allow 3 to 5 litres of black water holding capacity per person per day.  The larger the tank the longer you can stay at anchor.  We have about 50 person days capacity in total aboard Rockhopper.

I fitted a separate tank for each sea toilet to keep pipe runs short and simple.  Like all toilet pipes you must ensure that the pipes do not sag along their run or waste will become trapped there.


Each Lavac sea toilet and it's tank are connected via 38mm Y-valves allowing the following combinations using a Henderson MkV pump:

  • WC to Tank
  • WC to Sea
  • Tank to Sea
  • Tank to Tank (circulation for cleaning)



A 38mm deck extraction outlet allows waste to be sucked out at a pump-out station.  Each tank breathes through a 38mm Venus "Activated Charcoal" filter to prevent smells.  The extraction pipe and the breather pipe MUST be the same size or the shore-side extraction pumps will implode your tank.




There are many plastics companies offering a wide variety of both solid and flexible tanks.  However if you are retro-fitting your yacht, the 2 main problems will be finding space to fit a tank of any resonable size near to the WC and then finding a tank shaped to fit.  My solution was to look for a local plastic tank fabricator.  I modelled the tank shape I needed in thin ply wood with all spigot positions in place then had it "plastic heat welded" in thick black polyethylene.  

You will need 4 x 38mm hose spigots.   

  • IN from pump - terminating about 50mm inside the top face.
  • OUT to Pump - terminating as close to the lowest point in the tank as possible
  • OUT to Deck Fitting - terminating as close to the lowest point in the tank as possible
  • Deck Breather - terminating about 38mm inside the top face.

Don't forget to include a large access hatch in the top face for cleaning.   I didn't want any internal baffles which might catch waste so, during installation, I supported the base and sides with solid ply to ensure as little stress on the welds as possible when the yacht is pitching.   Your WC might look a bit like a wild "Triffid" when you are done, given all the valves and pipes, but make sure you have good access to all spigots as the white 38mm toilet piping has about a 5 year life and will need changing over time.   After more than 13 years of constant use both of our tanks still look like new.

In anchorages, we often capture our dish washing water in a bowl and pour it into the WC for pumping into the holding tank.  We calculate it as about one extra person each day.

When wintering in a marina there is a strong temptation to use the on-board facilities instead of going ashore especially in the dark.  We have stayed in marinas where that happens and it is horrible!   During the day its simple but at night we use the old "bucket & chuck-it" method, slopping out at the toilet block next morning.

Showers are usually well provided ashore but dish washing facilities rarely are.  Scrape as much food waste as possible into the bin, mop up oils and grease on kitchen paper before washing up.  Use a plastic bowl and pour into the night bucket when finished.   I know - it all takes at least 5 miniutes longer - which can totally ruin your day but you will save hours of polishing time if your hull doesn't get a slick of grease and oil at the waterline.

What Papers Do I Need To Have On Board?

What Papers Do I Need To Have On Board?

ESSENTIAL KIT - Over Bunk Fans

ESSENTIAL KIT - Over Bunk Fans