Found it!

I have been digging a trench to try and find the wastewater outfall pipe.  I dug a longish trench where I though it was and several metres either side.  I had no success although I couldn't see how it could possibly have been anywhere else.  I assumed, therefore, that the trench must need deepening although it was already significantly deeper than the depth of the manhole in front of the house.  I popped into the plumbers today to say that I was still looking and I'd place my order for the new en suite when I found the outfall.  One of the chaps there suggested that I use dowsing rods.  

Now I have a friend who dowses.  I'm not sure that he believes dowsing always works but I have seen many occasions when he has tried it when I've been there to witness it and it has worked.  As to why he has no idea and I certainly don't.  Scientific studies have shown that success with dowsing is no greater than the success of finding something by chance.  I wonder (as an aside) whether it has something to do with the person who is dowsing.

Anyway I decided that I had nothing to lose so I cut up a couple of wire clothes hangers, turned on the taps so that I had running water in the pipes and went forth and dowsed.  I walked around with the rods across the line where the drain had to pass below which included a little trench I'd dug after breaking an area of concrete.  It refused to work.  I went along the big trench I'd already dug and it  didn't work there either.  As the pipe had to pass somewhere there I decided dowsing wasn't one of my skills.  However I decided to give it another chance.  All of a sudden in a place where I hadn't walked before the rods moved inwards and crossed.

I decided there was nothing to lose by breaking more concrete and getting rid of some frustration.  About a foot down after having removed a considerable amount of stone over I came across a paving slab.  I removed a lot more concrete and stone and the paving slab and there, directly under where the rods had crossed was a manhole.

Well I still have no idea whether dowsing works or why the rods crossed at that point on this occasion but I found the manhole so do I really care?  No.  Not really.  Will I be offering my services?  No.  But I wouldn't rule dowsing out if I were looking for another water pipe.