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S&S Swan Maintenance - Holding Tank
03 February 2019 - 12:57
Join Date: 27 January 2011
Posts: 140

Holding Tank

Last summer I finally installed a holding tank on IF. The location originally foreseen for that on a 411 is forward starboard just next to the head. The only alternative I considered was to install it in the locker in the head, gravity-based, but in the end I went with Nautor's view, since installation and inspection/maintenance are easier there and it is possible to install a bigger tank. 

I did not find any off-the-shelf tank that would be a good fit, and had a company in Hamburg specialising in holding tanks build one from 10mm PE to my specification. This cost 900 EUR, including sensor, display and fittings. On top of that came a waste pump, Y valve, tubes, wiring, and switches. Installation was an entire day, plus another day for corrections later.

As you see from the photo, the 90l tank takes most of the available space. This was the place where I kept tool boxes and engine liquids. Initially I was at a loss of where to put all that, but funny enough it turned out that by removing superfluous equipment throughout the boat and starting to use the area under the starboard sofa in the saloon we ended up having way more space for food and personal belongings than we had before.

I have not yet installed a tube to the deck for emptying the tank in port. I rarely see pumps in the harbours we go to in the Med. The plan is to install it at some point later, using a second Y valve directly on top of the tank.

In the photo below you see the waste pump installed next to the basin in the head. Pump and toilet exit go to an Y connector shortly above the sea cock. I (so far) did not manage to route the tubes in a way that allows to screw the Y valve onto a wall, so it is free-floating at the moment. In return I managed to retain most of the space below the basin.

A second sea cock for the waste pump exit would have been better, but the approach with the Y connector works just fine.

The tank fittings are well above the waterline.

In the meantime I have changed the ventilation, the filter now being higher up to avoid problems when heeling. The exit of the filter connects to the ventilation of the shower sump in the head, which is convenient. I may eventually move the filter into the upper left locker in the head.

The five of us went onto a 2-month cruise from Marseille to Scarlino via Sardinia last summer with this setup. As expected this turned out to be a significant improvement of live on board.


Christian 411/028 IF


05 February 2019 - 20:54
Join Date: 19 July 2007
Posts: 66

GHi Christian.

Thanks for your interesting post.

We have been looking into installing a holding tank into our 411 Hierro,  and like you have not found a standard tank that will fit into the boat and provide sufficiet volume.

Can I ask the following.

Do you have the original "Baby Blake" WC. Does all the waste pass into the holding tank, to be pumped out or can it be pumped directly from the WC, to the sea via the Y valve? Does the tank extend to the bottom of the locker, I note it is bolted to the inner bulkhead at the top, is it supported from the bottom. Do you have the dimensions of the tank that you could share?

Thanks Again.


Hierro 411 042

06 February 2019 - 18:45
Join Date: 27 January 2011
Posts: 140

Hi Paul,

we have a standard Jabsco head with manual operation. With the Y valve we control if waste goes to the tank or to the sea. When selecting the sea, it goes from the Y valve to the Y connector you see on the photo. There is the risk that it goes up to the pump, via the other branch of the Y connector, but we have not observed that. This would probably only happen if the sea cock is closed. The pump is above the waterline.

The tank sits on the original board in that space and is screwed to the wall in two places as you see on the photo. This way it is squeezed in and not moving in any direction. 

I sent you a message, happy to share the plan!

Christian 411/028 IF


24 May 2019 - 09:37
Join Date: 20 July 2017
Posts: 115

Hi all,

since we recently (Winter 2017/18) also refitted a holding tank on 'Kairos' (57-43) I thought we'd share some of our thoughts and the specs/approach, which you might find helpful... The work was carried out by Yachtwerft Glueckstadt, Germany.

Main reason for the installation of a holding tank was to comply with regulations in the Baltic and elsewhere.

Kairos has three heads (two fwd, one aft) but we decided that one holding tank for one of the heads must suffice. We also didn't want to use too much of storage to the tank, especially not storage that is easily accessible.

Being paranoid about potential leaks in the holding tank system that are difficult to get to we also didn't want any connections on the bottom of the tank, which ruled out a gravity system.

Based on all the above and being the most 'comfortable' head to use, we chose the aft head as the one to get the holding tank. The fwd heads remain but can only pump straight to sea; if need be we might have to 'disable' them to comply with regulations but that bis not required for the Baltic. The tank is located in fwd locker in the head, so we lost that for storage, but as the tank goes all the way down behind the wash basin top we also utilised a lot of otherwise unused storage. 

That way we managed to get a tank with about 150l of usable volume but only lose one locker, which tends to be suffcient for a crew of 7 for 3-4 days of use.

Tank was made to measure (maximum size) and welded of 3 mm A4 stainless steel (1.4571) with a screwed on inspection hatch near the top. It might be worth noting that the shipyard made a cardboard model of the tank first to ensure it would fit through doors and was installable. Two pipes for emptying the tank - one for overboards emptying via a Jabsco 12 GPM waste pump (18590-2094) and one for emptying via the deck in a marina. Tank utilises an existing vent through the hull with a Dometic DVF 1619 filter.

The tank is connected to the head via a Y-valve (Jabsco 45490-1000), which enables us to select wether the head pumps straight out to sea or into the holding tank. System als has a non-return valve (Jabsco 29295). 

Level indicator is a Gobius 4, which is non-invasive i.e. no holes required for the senors.

All hoses used are 38mm Vetus waste hoses.

We had the system in use for two seasons now, all working very well and the capacity seems more than sufficient. The tank is virtually invisible as the original door of the locker was re-installed - only the display of the Gobius is visible.

Emptying via the Jabsco takes some time, and it is a bit difficult to know when the tank is empty (basically you have to listen to a change in the noise of the pump). The level indicator only has three levels 'empty', 'half full', and 'full' so not useful as an indication when the tank is really empty. However, as the Jabsco is a membrane pump running dry isn't too much of a problem though if we miss 'the right moment'.  We have yet to test emptying via the deck/a marina... need to find one that can accommodate a draught of 2.85m first 

Have attached a few pictures, hope you will find this useful.

All the best,


SY Kairos


Tank in its location in fwd locker next to wash basis; vent filter can be seen on top, Gobius level indicator on the front

Actual tank size; goes well below top of wash basin using inaccessible space; tried to have a manhole that is of useful size and as high up as possible

Sketch of system, we have an electric pump to empty the tank

25 May 2019 - 09:40
Join Date: 02 February 2007
Posts: 202

Hello dear S&S SWAN Fans!

From my own experience using a stainless steel holding tank: never add any of those special chemical products for holding tanks if you have a stainless steel tank! They are really great for corrosion! We had a leak after just one year of use! Just rinse them with fresh or salt water from time to time. I understand the best solution is polypropylène as Chris seems to have.

Also using the original Blake toilet is no problem, membrane Jabsco pump is great for emptying.

Fair winds. Philippe 41/022.


25 May 2019 - 19:40
Join Date: 02 January 2008
Posts: 1547

Dear Philippe

I would like to ask if the holding tank corrosion occurred in a weld? Was the tank re-welded, or how did you solve this?
Kind regards

26 May 2019 - 07:06
Join Date: 02 February 2007
Posts: 202

Dear Professor,

yes the leak occured at a welding point in a corner. I had it rewelded and reinforced with an L shaped stainless steel profile. Of course I had to take the tank out which was no great fun. If I had to do it again I would go for a custom made polypropylene tank.

For the air vent I used the original piping venting the other tanks to the back of the boat. No problem with smells!

Kind regards.



26 May 2019 - 07:33
Join Date: 02 January 2008
Posts: 1547

Dear Philippe

Improper choice of stainless material and welding details is likely to be the reason for your tank weld corroding so quickly. 
There was a discussion on the Forum about this subject over 10 years ago.
Unfortunately welded stainless is not always stainless, but good welding shops should be aware of what is required to avoid these problems.
Kind regards

03 June 2019 - 14:03
Join Date: 20 July 2017
Posts: 115

Dear Philippe and Lars

thank you very much for your feedback and sharing your experience - we haven't had any problems with corrosion so far but obviosuly are only in the very early days of usage (2nd season).

Luckily (from what you wrote) we do not use any 'holding tank conditioners' but the tank will obviously see some (diluted) chemical cleaning products via the usual toilet cleaning process.

We are in the fortunate position to have a fire water pump on board and regularly flush the tank with seawater via the deck opening, which is very convenient.

Together with (what we have been told) good weld quality from an experienced welder I hope we'll be ok ... fingers crossed!

Of course our the system would work in the same way with PE as tank material - we did actually would have preferred PE but that would have meant maufacturing it elsewhere i.e. without the benefit of a good local relationship of our boatyard with the manufacturer/welder. Guess time will tell if that was the right decision ...

All the best,


Kairos 57-43

03 June 2019 - 14:10
Join Date: 29 January 2007
Posts: 1018

Dear Stefan and Friends,

I have a custom built PE holding tank, even if I would have preferred a stainless steel!

Anyway, it works!

As Christian, I have not yet installed a tube to the deck as I haven't seen many Mediterranean marinas with emptying pumps. But it could be installed anytime!

Fair winds!

matteo (47/069 Vanessa)

05 June 2019 - 16:05
Join Date: 15 April 2011
Posts: 393

Dear Matteo,


Do I understand correctly that boats in the Med have holding tanks that cannot be easily emptied?  So, are they filled and then emptied into the sea?

Here in the Chesapeake Bay, east coast of USA, pump out stations are abundant.


Chris, Mabel's Casse Tete 43/003

05 June 2019 - 16:07
Join Date: 29 January 2007
Posts: 1018

Dear Chris,

I know this is a nonsense...but unfortunately it is correct. Just a few marinas, private and not public owned, are organized to empty holding tanks.  (no comment).

Fair winds

matteo (47/069 Vanessa)

05 June 2019 - 16:43
Join Date: 15 April 2011
Posts: 393

Thank you, Matteo, for the clarification.  Fair winds to you my friend! 

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