I found this on a photo site:
Piping Tip:
=95 All pipes are made of a long hole, surrounded by metal or plastic.
=95 All pipes are to be hollow throughout the entire length, do not use holes longer than the length of pipe.
=95 The inside diameter of the pipe must not exceed the outside diameter of the pipe, otherwise the hole will be on the outside.
=95 All pipes are to be supplied with nothing in the hole, so that water, steam or any other stuff may be put in at a later date.
=95 All pipe should be supplied without rust, this can be added later on the job site. N.B. Some vendors are now able to supply pre-rusted pipe, if this is available in your area it may save some time on the job site.
=95 All pipe over 150 meters in length should have the words "long pipe", clearly painted on each end, so the contractor will know that it is long pipe.
=95 All pipes over 1 kilometre long must have the words "long pipe", painted in the middle, so the contractor will not have to walk the entire length to determine whether it is long or short pipe.
=95 All pipe over 150mm inside diameter must have the words "large pipe", painted on it, so the contractor will not mistake it for a small pipe.
=95 Flanges must be used on all pipe, the holes in the flange must be separated from the big hole in the middle.
=95 When ordering 90, 45 or 30 degree elbows make sure you specify right or left turn; otherwise you will end up having the pipe going the wrong way.
=95 Be sure to specify when you order the pipe, whether you want level, uphill or downhill pipe, otherwise if you use uphill pipe for going downhill, the water will flow the wrong way.
=95 All couplings should have either right hand or left hand threads, but do not mix the threads, otherwise the coupling being screwed on one pipe is being un-screwed from the other.