The dishwasher waste water outlet connects to the sink draining pipe 'V' with the usual rubber connector and metal tightening clamp.

I'm getting some back-siphonage as the exhaust pipe is not high enough, but due to the situation, the pipe is not long enough.

Where can I get a piece of piping from which would be suitable to extend this and perhaps one which has a valve so that I can physically close off the piping if required.

Your "Back siphonage" might be a partially blocked drain pipe.
A plumber here is called a Sanitaire.

http://yellow.local.ch/en/q/?what=Pl...id=directories

http://yellow.local.ch/en/q/Sanitaire.html?rid=LyL8

If you don't want to hire a Sanitaire, then go to Migros or Jumbo or Coop do it your self shops.
Or look for Baumarkt supermarkets.

I've seen this problem before. From what I understand there is water going from the sink back into the dishwasher because of the V connector?

There are one way Y connectors you can buy at DIY shops, where the water coming out from the sink and dishwasher only travels one way through the valve. Just google for your nearest Coop Bau & Hobby.

It sounds like your sink waste pipe is blocked (syphon).
The dishwasher outlet is higher up than the water level in the syphon (wall outlet). That is why normally the water from the sink does not run towards the washer.
How old is your dishwasher?
If it is older than 15 years or perhaps a cheap model it could need a "non return flap" in the entrance to the syphon.
Take a look here on page 9 left hand side.http://download.geberit.de/ch/Montag...d_Zubehoer.pdf
A modern dishwasher has this "non return flap" built inside the washer next to the waterpump. The waterpump is installed to pump out all the water from the pipe (it pumps until there is no back presure).
You hear this when you start a new wash.
There will always be a rest of water in the washer, inside the salt container. This also leaks out into the bottom of the washer.
I do not think making the pipe longer will help.
If you need to make the pipe longer, go to Fust and ask for a "Waschmaschine Ablauf Verlengerung". They are standard size for all wash and dishwashers.
Hope it helps.

Salut Zämma

Bauhaus or Hornbach definitely have the part.

COOP Bau+Hobby or Migros MMM might

could be. any ideas how much it would cost to call them out and fix this. i'm quite wary of being switzerlanded.

Phil, do you know if the problem is in the machine, or in the wastepipe?
If it is in the machine, the plumber will just shake his head and send you a bill for his wasted time (switzerlanded, what a stupid word).
I take it from your reply, you are no DIY type.
Why do you not check first where the problem could be.

Check that the machine pumps all the water out and it does not run back.

Take the floor filter out of the machine and fill the machine with 3 ltr water and close the door. Now start the machine, you will hear the pump working.
As soon as the pump as stopped open the door again very quickly.
If the problem is by the machine. you should now see water running back from the pump into the filter hole.

Now the 2nd test, fill the sink with water up to the overflow.
Open now the drainplug and let the water out.
Check in the machine if the level of water rises. If this is so you need some one to service the machine.
If the water runs slowly out of the sink, but not into the machine, then you need a plumber (I think).
Best of luck with your 2 left hands.
Salut Zämma