Coolant and Heating main pipe leaks
note:Outer/offside pipe is return, inner is send (to radiator)
Use Clips either the Mikalor T bolt variety or the original VW spring clips. http://www.advancedfluidsolutions.co.uk/mikalor-w2-stainless-supra-hose-clamps-119-c.asp Mikalor
The spring clips are harder to fit but allow rapid expansion and cooling and apply even pressure and are not possible to over tighten. There is a hose clamp removal tool available from GSF but a long nosed mole grips or water pump pliers will do the job too.
also see go westy 
Rear of pipe Hacksawbob I put amalgamating tape around the metal pipe and whacked it home there is no way thats coming out again. My problem was that (and this may be quite common) that outer hose is used as the drain point, with the constant on and off at this point the pipe has become brittle and cracked. hose clips are used instead of the original spring clamps. These can and are tightened up too far possibly distorting the metal and/or cracking the plastic. I seated the metal insert with tape then got a length of rubber coolant hose from Halfords, this was slightly longer than the hose that goes from the plastic 'tree' (distribution connector) to the long plastic pipes It was a perfect fit and length so I just added one o ring between the metal lip and the plastic body then put 2 hose clamps on the first one I tried as best to seat it on the rubber O ring.
The part I used to replace the VW hose on the outer pipe (return)from Halfords was a 38X311mm (311mm long dia 38mm) Part number HFH203 Flexible water hose. internally it has a metal spring to enable it to bend without kinking.
Front of pipe
This is best done with the van on drive on ramps or jacked and supportd and with the spare wheel carrier removed.
The front pipe had cracked as above. This time I made up the distance between the end of the pipe with a short length of rubber hose ideally you would use a rubber hose that was the diameter of the metal pipe I couldn't find any so I used short sections of 19 heater hose crammed onto the metal then wrapped in tape leaving about an inch to get seated into the old plastic pipe. Again I wrapped self amalgamating tape around the end metal insert then whacked it home and taped over the join. Seems to be OK for now. I used a jubilee clip and a sprung ring seen in the picture to hold it all together. Update, this fix lasted for about 2 months then I had to bite the bullet and replace the whole pipe. The rear repair (as described in the top section) is still going strong on the other van.
The steel inserts are cast in place to reinforce the tube ends under the hose clamps. The nylon casting around the barb cracks, and due to the pressure inside the cooling system the sleeves, hoses and clamps gradually walk off the pipe. This often happens only on the hot (feed) side, not the cooler return pipe. GoWesty has their clever kit, whether or not it works is controversial, but what is known to work is to remove the sleeves that are coming apart, they will withdraw easily if you warm the plastic with a hot air gun first. Then wire-wheel all the corrosion off the sleeves, roughen the outer surface of the sleeve and the inner surface of the pipe with coarse sandpaper to give the epoxy something to key into, apply a thin coat of JB Weld or other HD epoxy of your choice, warm the pipe end again and slide the sleeve back home.
Some people add a couple rivets thru both where the hose will cover them, belt and braces as it were.