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      Dear Fellow BOA members

      Yes its the good old holding tank issue, does anyone have a specific descaling product they can recommend ? I have found that lime scale (I assume) has developed on the inside of the holding tank, small pieces breaking away are big enough to block the outlet pipe at the base of the tank. Access to the removable inspection hatch is limited by the space between the top of the tank and the deck head in my Bavaria 36 therefore I need some kind of chemical solution to dissolve the scale and flush it away.

      Any suggestions ?



        Hi Andy.
        Watch out for the next news letter…….. I think Bob has a couple of tales to tell doesn’t he Bill?

        It is a major problem with the plastic tanks. As they flex and the pipes flex the lime scale is dislodged. Empty the tank as much as possible. then get a pump out with the sea cock open or if your brave use an aqua vac to do the same. Keep emptying the vac until you get clean sea water and no lime scale. Close the se valve and fill the tank with fresh clean water. Then use this stuff http://www.plumbworld.co.uk/saniflo-cleanerdescaler-5l-510-29422?utm_source=GoogleBase&utm_medium=GB&utm_campaign=GoogleBase&gclid=CJS8oLGSh88CFQdAGwodJrwBbA

        Follow the instructions carefully, it is acid!

        Best regards




        I think it is you and Bill that have the stories to tell (and an article to write). I was just seen sitting in the corner and chuckling.


          Hello everyone, one of my favourite topics 😯 not!
          A couple weeks ago my tank became blocked. We were very remote on the west coast of Scotland near Skye, tank full and could not access the inspection hatch because the stainless steel tank is fitted in the engine room very close to the ceiling.
          Then I had a brainwave, I opened the deck plug and using a piece of hose (cut off from my main freshwater filling hose, and never to be used for this purpose again) I shoved it down the plug hole all the way to the tank a bit like a drain rod. A few ups and downs and voila, the tank started draining.
          Hope this helps!!


            A tale of woe and a holding tank
            Before I get started there are a few concepts that you have to understand.

            • Its not possible to compress black water in your holding tank.
            • However, you can compress any air in the pipes or the top of the tank.
            • Under pressure from the toilet pump the tank and the pipes will expand if the sea valve is closed or there is a blockage.
            • Under compression the holding tank will inflate like a balloon, acting as a reservoir.
            • On our B37 there is no facility to divert black water straight from the toilet to the sea, it has a single ball valve that either opens the tank to the sea or not depending if it is open or closed. (Some older boats have a Y valve that allows you to divert the waste directly to the sea avoiding the tank).

            The layout of Impavidus’s holding tank .
            [attachment=2:35l19qsi]Holding tank.JPG[/attachment:35l19qsi]

            So, to tale of woe…….

            The holding tank sensor on Impavidus has never worked. Clipper have replaced it twice but it still gives false readings and sets off the tank alarm. So we disconnected it at the sensor and keep an eye on the tank level through the access hatch. Generally we keep the tank dump valve closed. Only opening it to empty the tank when we are well away from land.

            This year we took 3 weeks off work in the summer to sail across to the continent with the idea we may get down to the Med and leave Impavidus there so we could fly down to her on Easy jet or the like. The weather had been really good for a few weeks, the boat had been provisioned and made ready in the evenings of the weeks before. On the Friday evening after work we sailed down to Lymington hoping to get a sling shot with the tide down to Dartmouth then across the channel . On the Saturday morning the forecast worsened and a big Atlantic low started dumping rain and even hail stones on Lymington. Winds were forecast up to F8 in open water so, needless to say we stayed put…… With the holding tank valve closed.

            In the town we did the usual market thing and some shopping in Tesco. I even brought on of those Toilet duck dispensers that put a rose shaped gel on the toilet bowl. That will keep the air sweeter in the heads I thought…….. I did not read the instructions, it a bloke thing, you only read instructions when all else fails or something goes wrong?

            After 3 days the weather turned again and we set off for Dartmouth. However, the sea state was horrendous, with big swells and breaking waves through the needles. Even though the wind was a gentle F3-4. We decided to put in to Studland and wait for the swell to abate. After all we had 3 weeks? We crossed Christchurch bay, which was quite lumpy especially where the water shallows over the ledge. As we were quite close to land in shallow water the holding tank valve remained closed.

            Next morning we were woken by the battery alarm telling us the house batteries were low. At the time I thought little of it as we had been using power for the TV/DVD, fridge, lights, anchor drag alarm etc, etc. We motored off around old Harry and Cindy made a bacon sandwich and a coffee. The wind was F3-4 with the possibility of F5 later or around exposed headlands.
            As soon as the bow cleared the cliffs at Swanage the swell got up again with really quite big seas breaking over the bow on the starboard side. By the time we got to Anvil point we had had enough wind on the nose and a hard beat to make headway. I turned Impavidus round and we headed for Poole. After all we had 3 weeks…..

            A night in Pool quay yacht haven, a meal out and the chance to get a good forecast, look on the web at the wave heights, and give the batteries a good charge seemed the best idea. At for £52 a night including electric, a bargain!!!!! After our evening meal and some web surfing. We decided that we would coast hop down to the Scilly isles. Via Salcombe, Fowey, Falmouth and Newlyn. Leave the Med for another year.

            Setting off the next morning we were in Ideal conditions. The wind had turned over night and a F4-5 North Westerly took us romping across Lyme bay and into Salcome. While out in the bay we opened the seacock on the holding tank. I remember thinking that it emptied quickly. The aqua blue and special toilet paper at £2 a roll must be helping………..

            We were still having to run the engine every 4 hours or so, as the batteries did not seem to be coping with the loads we were putting on them when sailing. But we were on holiday and I did not worry about it.
            We got in to Falmouth, the weather was holding and we had some fantastic days getting there.

            Falmouth Marina is away from the town, but being a Premier marina it is a free night for us. We decided to stay the next day too, go into town for provisions and of course you cannot go to Falmouth without a visit to Traygo mills?

            That evening we noticed the holding tank was full. The toilet was difficult to pump and the breather tube actually had black water coming out of it.

            Ooops, funny that, because we emptied the tank before we came in to Falmouth ?????? Anyway I decided to empty it again on the way to Newlyn the next morning.
            We cleared Falmouth early and well off shore I opened the valve. There was a gurgling sound but no slick behind us. I gave the toilet a few pumps but the result was black water coming out the breather for a minute or two then nothing. I then went to check the tank level. But the tank was swollen and I could not get the access panel off.
            Ooops! After another hour or so of sailing we decided to return to Falmouth and get a pump out at Premier, after all it would be free………. And those batteries were very low again.

            Thinks; “Best to head back and sort it where we have all the things we may need easy to hand. Newlyn is a proper fishing port and we know there is just about nothing for the cruising sailor there”.

            Back in the same birth as the previous two nights by mid-day, I discovered Falmouth does not a pump out facility. Not Falmouth marina, Falmouth the port not one! The nearest was back at Fowey…….

            Ah ha thinks; “I can make my own pump. Cannot be difficult after all it’s probably just some paper blocking the bottom of the tank?”

            I got up the chandlers and £35 later I had a large dingy bailing pump some fittings and various off cuts of hose that would enable me to form a seal between the pump out fitting and the large bore of the pump. A extra metre of 40mm hose for the outlet of the pump that would allow me to pump the waste over the side effortlessly?

            We could not get out of the marina until 17:00 hrs as the entrance is pretty shallow. So I decided to have a look at those batteries. I found nothing lose or missing and being just a year old AGM batteries there was no top-up holes so it must be something else? Probably? At 17:00 we left the marina telling them we would be back in an hour or so and not to allocate our berth.

            Clear of the Harbour entrance and about 4 mile off land, Cindy held Impavidus into the waves on tick-over and I went on deck to remove the pump-out cap.(Its at this point you may need to refer to the my first paragraph again).

            Thinks; “Crikey that cap is tight”. But it started to turn, half a turn, one turn, two turns and nearly there………. Whooosh!!!!!!

            Now the holding tank when full, holds 75 litres. It was at that precise moment I remembered something about not being able to compress a liquid, and how when I was a kid, the lady next door had forgotten that the pressure cooker was on and it exploded putting its entire contents of beef stew in to an interesting collage of colours across the entire kitchen.

            Cindy was in hysterics. I must admit my newly delivered sewage farm camouflage outfit must have looked quite good. Unfortunately it did not smell that great, and it had run into my flip-flops too. Nothing for it, I stripped off and standing on the side deck in my jockeys and bear feet attached the pump to the outlet and started pumping. The swell offshore was only ½ a metre or so, but it was enough make holding the pump on the outlet and standing upright quite a challenge. Indeed several times I did not quite achieve verticality and full pump contact…… You can guess the result.

            After twenty minutes of pumping, or what seemed at least that time, we were not seeing any sign that the tank was empty. And there was still that gut wrenching smell. Cindy went below and was able to remove the access hatch. The tank still appeared to be half full. It was at this time that 4 guys in a speed boat who were fishing ½ a mile away decided they would go and see that lovely sailing boat with the strange guy in a pair of pants feeding a flock of seagulls was doing. They got to within 50 yards before the first one started heaving over the back of the little Fletcher. They sped off pretty quick.

            It was then I decided this was not that funny, well not really funny. Cindy turned the inverter on and passed up the Aqua-vac. My brain wave was to use the vacuum to pump out the tank the way it was designed to work. It would mean having to empty the contents of the Aqua-vac into the sea a dozen times or so? But hey, it could not get worse could it?

            The answer is yes, it could! Remember I said we had prepared the boat in the evenings before we left? Given Impavidus a good clean, hovered up the dog hairs, all that fluff and dust that seems to come from nowhere on a boat? It is amazing how much there is? Hummm ! The Aqua-vac as I opened it, in the rolling seas, on the slippery deck, in the light breeze, deposited its contents all over my new camouflage suit! I was now the sewage equivalent of tarred and feathered!

            Sometime later the hover started to show signs of clear water in the bottom although there were strange plates of lime scale in there too. Another few bucket loads and clear water was being sucked up through the outlet, into the tank and into the Aqua-vac. Job done.

            A shower off the transom and some disinfectant on me and Impavidus returned us to
            some level of normality and eventually back to Falmouth marina.

            Lessons learned ?

            • Well you should always read the instructions.
            • Toilet duck contains a descaler, very good at removing big lumps of lime-scale from holding tanks and their associated pipes and plumbing.
            • These fall to the bottom of the tank and very effectively block the waste outlet.
            • When the tank is full if you keep pumping the black water will come out the air vent along with any solids, until that too blocks.
            • If you continue to use the toilet pump, even with a dry bowl, you will pressurise the tank.
            • If the tank is pressurised and you take the lid off you will wear the contents of the first ¼ of the tank.
            • Sailing is the most fun you can have with your clothes on.
            • Exide AGM batteries are not as good as you may think, but that’s another story…….

            Impavidus: 2015 Bavaria Cruiser 37.

            Anthony Kirkby (Vice Commodore BOA)


              Hilarious read. I almost felt I was with you reading this. One thing you can say about sailing is it makes you resourceful and your story proves that point very well!! Guess you’ll be getting a Y valve installed next lift out?


                Thank you all for the replies and the laughs !

                Will try the acid option to dissolve the scale. Prevention better than cure……my story…..

                When I suffered the fate full blockage my shipmates (ships engineer and chemical plant engineer) decided to employ the inflatable dinghy pump to pressurise the tank via the pump out point on deck having used a wooden bung to block the tank vent in the anchor locker. The question arose of how to de-pressurise as the blockage remained, the question was answered when the foot pump pipe shot out of the deck outlet, remember those ‘indoor fireworks’ !

                A length of clear braded plastic pipe, a wetsuit and safety line were the next weapons of choice. As I avoided the on deck muck spreading I drew the short straw and went over the side. The pipe was flexible enough to take the bend in the seacock and after some pushing and pulling the sniggers on deck revealed that it was working as a dark brown slick was seen developing around me, having my safety rope tied off on the midship cleat I had no means of escape until my so called shipmates gave me some slack, due to uncontrolled laughter this took some time !

                After a few beers and yet more laughter we decided another emergency back option was needed. When in the next marina I purchased a length of plastic shroud wire cover, following removal of the inspection hatch on top of the tank, there is just enough clearance under the deck head to feed the plastic tube (flexible too) into the tank and gently tap it up and down to break the scale up so that it cleared the exit point of the tank. Later in the trip it appeared that the tank was not doing the usual Niagara falls trick, we tried the shroud cover piping and it worked. All clear, no explosive turd, tank has been good as gold since.


                  A story for the back page of YM.
                  We laughed and giggled at this.
                  Every time we go down to the boat we will look over at Impavidus and smile at the imagined figure on deck.
                  When in the BVI we emptied tanks (3) every time we were offshore BUT we didn’t realise that the crew cabin in the bow of our Beneteau 505 did not have a tank.
                  One member feeling a bit iffy did not want to use the family head aft so went forward.
                  A day or two later our friends in the port forward cabin asked us if we had a funny smell in our ( starboard forward ) cabin.
                  No we said.
                  The son-in-law of the aforesaid user of the forward head then opened the hatch to the crew cabin in the bow.
                  He reeled back .
                  It appeared that father-in-law had pumped against a closed seacock and the compressed efluent had been festering in the Carribean heat.
                  Having released the pressure he emerged looking slightly green/yellow the only cure for which was a large rum.
                  Port Solent

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