I must say on reading this post i am thinking what is the point.
On new build or for extentions the drawings are supplied and if the builder or archietech wants an as is pipework drawing i do it on one of theirs in pencil. No one else ever gets a drawing because they don't require one and i am not being paid for it. Gas line diagrams are never required for domestic stuff.
If they want to know where the pipes are in 10 years time phone me and for a small fee i'll do my best to remember :lol:
I understand that for most private jobs you would not need drawings. if you wanted to get work with any builders that builds for local landlords and housing bum. you would have to be able to produce drawings to a decent standard and provide design specifications and liabilty. Pencil lines are not good enough for most builders that have promissed there client professional drawings. I guess it depends on what work you are going for, to be able to produce drawings is another selling point in an ever competitive and tight market space.