All pipe is to be made of a long hole, surrounded by metal or plastic centered around the hole. All pipe is to be hollow throughout the entire length - do not use holes of different length that the pipe. All pipe is to be supplied with nothing in the hole so that the water, steam or other stuff can be put inside at another date. All pipe should be supplied without rust - this can be more readily applied at the job site.
Some vendor are now able to supply pre-rusted pipe.
If available in your area, this product is recommended as it will save a lot of time on the job site. Flanges must be used on all pipe. Flanges must have holes for bolts quite separate from the big hole in the middle. Be sure to specify to your vendor whether you want level, uphill or downhill pipe. I you use downhill pipe for going uphill, the water will flow the wrong way.