# How do you drain down your water tank?



## Morphology (Jul 23, 2010)

We have a Knaus Sun Ti and, as it starts to get colder, I want to completely drain down the system. I can open taps, dump valves etc and run the pump until empty, but I always end up with a puddle of water in the bottom of the tank (see photo). 

The tank has a 'sump' area in which the pump sits, and a vertical overflow pipe sits in the only hole in the bottom - there is no separate drain valve.

Sometimes, if I can be bothered, I stick a hosepipe into this puddle, suck on the other end and syphon the last dregs out, but this is tedious and messy so often I don't bother and I'm concerned that if the puddle freezes it might damage the pump, plus it's a great environment for bugs to breed so I'd be happier if the tank were completely dry.

A while back I read an article in MMM about prepping your van for winter and, to accompany the article, they showed a picture of somebody removing the vertical overflow pipe in a tank identical to this one.

However, our overflow pipe doesn't seem to simply pull out. I don't want to break it by pulling too hard and there isn't really room to get your arm in there with a spanner to loosen off the locking nuts.

Is it supposed to unscrew or pull out?

Incidentally, the 3rd photo shows my solution to the problem of water sloshing out of the overflow whilst driving along (we can sometimes lose up to a quarter of a full tank whilst driving) - the bung is from one of those vacuum wine preserver thingies, and fits nicely into the top of the overflow pipe.

Morph.


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## andrewball1000 (Oct 16, 2009)

Morphology said:


> - there is no separate drain valve.
> 
> Sometimes, if I can be bothered, I stick a hosepipe into this puddle, suck on the other end and syphon the last dregs out, but this is tedious and messy so often I don't bother and I'm concerned that if the puddle freezes it might damage the pump, plus it's a great environment for bugs to breed so I'd be happier if the tank were completely dry.
> 
> ...


Morph. The vertical pipe unscrews, anticlockwise. There is an o ring on the bottom but the tank moulding is very rough as the metal seating on the tank was designed for an external take off. It cut mine up badly so I removed the whole assembly and replace it with a lever ball valve drain from underneath. I will post more details if you want. It also overcame the problem of the drain overflow half emptying the tank as I drove.


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## andrewball1000 (Oct 16, 2009)

This is my equivalent of your bung that I used prior to replacing the overflow assembly. It is a one way flap valve from a swimming snorkel and allows air to enter as the water is used.


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## Morphology (Jul 23, 2010)

Brilliant, thank you!

That's exactly what I like about these forums - ask a question and somebody pops up with the answer.

I'd given it an experimental twist in the past, but nothing seemed to budge. Your post gave me the confidence to get both hands in there and give it a really good twist and, sure enough, it unscrews.

Your anti-slosh solution is rather more hi-tech than mine, but the result was probably the same.

Yes, I'm interested in your ball-valve solution if you've the time/inclination to post, though the bung is working pretty well.

Richard.


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## andrewball1000 (Oct 16, 2009)

Hi Richard,

I found that regular draining was rucking up the O ring on the overflow pipe and also on the top cover.

I removed the pipe entirely and added one of these from the bottom. http://www.screwfix.com/p/full-bore-lever-ball-valve-15mm/80413 I think it was the 15mm but not sure. It had a 1/2" BSP thread which is what the tank exit is.

I also added a brass version of one of these first a 1/2" male to female 45degree bend http://www.alibaba.com/product-gs/446618337/45_degree_elbow.html which I got from a yacht chandlers. It was necessary to cant the valve over to clear the chassis below.

Now I can reach the lever externally just forward of the wheel arch and behind the waste water drain lever and draining is a very simple matter and both drain in the same footprint which is handy if over a drain cover.

I was concerned about creating a vacuum when draining so added a flexible open pipe from the inside of the filler up behind the the seat cushion. I don't know if this was necessary but played safe. Maybe some else can give some advice on this.


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## Morphology (Jul 23, 2010)

Andrew,

many thanks for takign the time to post the details of the drain-down mod. I'll see how I get on now I've been able to remove the vertical overflow pipe, but it's worth knowing what the alternatives are.

Richard


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## dealgan (Jun 26, 2006)

This is interesting !

I tend to lose nearly half my fresh water in transit, so have been looking for some way to stop it all leaking out.

Where would I find one of those flap valves ? (apart from the obvious !)


Thanks,
Declan


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## bktayken (Oct 11, 2008)

Had the same problem draining the tank till Andrew put me right .Also have valve fitted to the underside of the drain so now when I fill no need to remove the cushions or tank top ,just open the valve and it over flows when full then just close the valve and you have a full tank and no loss when driving.

There is a breather connection on the inside Andrew I have plastic tube tucked up behind the cushions work well.


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## dealgan (Jun 26, 2006)

Thanks for the pic.

How does that hose attach to the hole in the tank bottom ? or am I missing something ?

Thanks,
Declan


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## andrewball1000 (Oct 16, 2009)

dealgan said:


> Where would I find one of those flap valves ? (apart from the obvious !) Thanks, Declan


I just Googled Images Snorkle valve and got this link There are others) http://www.mailsports.co.uk/accessories/training_aids/product~2037

It is the initial one I initially used till I replaced the whole assembly. It nearly fits the pipe and will do so if you warm the top of the pipe with a heat gun and open it slightly.


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## andrewball1000 (Oct 16, 2009)

dealgan said:


> Thanks for the pic.
> 
> How does that hose attach to the hole in the tank bottom ? or am I missing something ?
> 
> ...


The bottom of the tank is 1/2" BSP thread. See my earlier post


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## rosalan (Aug 24, 2009)

After all water that will drain out has gone, I put an airline gently to the taps until all the water has left the system.
If you have a flush cassette toilet, that also may need draining if it has its own tank. I always find this task rather messy with cold water trying to get into the cassette area after pulling out the bung.
Alan


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## bktayken (Oct 11, 2008)

dealgan said:


> Thanks for the pic.
> 
> How does that hose attach to the hole in the tank bottom ? or am I missing something ?
> 
> ...


Hi Declan the tube is a perfect force fit into the overflow tube and I sealed it with silikone ..and you can still remove the overflow tube from inside if you want not that there is any need too .


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## andrewball1000 (Oct 16, 2009)

bktayken said:


> Hi Declan the tube is a perfect force fit into the overflow tube and I sealed it with silikone ..and you can still remove the overflow tube from inside if you want not that there is any need too .


Hi bktayken, I dont understand why you have left the overflow tube in position as surely you will still have to remove it to drain your tank, or am I missing something here? If you remove it then your new tap will both stop water loss when driving and allow tank drainage without removing the top tank access cover.


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## bktayken (Oct 11, 2008)

andrewball1000 said:


> bktayken said:
> 
> 
> > Hi Declan the tube is a perfect force fit into the overflow tube and I sealed it with silikone ..and you can still remove the overflow tube from inside if you want not that there is any need too .
> ...


The overflow tube is still in situ so I just unscew it as normal to empty the tank ...the rubber tube only goes up the over flow about half an inch so the tank still drains fully


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## andrewball1000 (Oct 16, 2009)

bktayken said:


> The overflow tube is still in situ so I just unscew it as normal to empty the tank ...the rubber tube only goes up the over flow about half an inch so the tank still drains fully


OK I see. I fitted the drain plug below the tank and removed the overflow altogether so it is very simple to drain from outside.


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