This section is from the book "American Plumbing Practice", by The Engineering Record. Also available from Amazon: Plumbing: A working manual of American plumbing practice.
The direct or main tank supply should have branches to all fixtures and to hot-water boiler. The boiler may be of galvanized wrought iron or tinned copper. The boiler should have a valved sediment pipe for emptying, and this should be opened at intervals to remove the sediment deposited in the boiler. The sediment pipe must not connect directly with the house drains
All branch lines must drain completely. The hot-water riser, if the water service is from a tank, must have an expansion pipe extend over the top of the tank and raised well above the tank.
Branches should have a stop-cock, and wastes and runs of pipes should have brass unions to admit of ready repair.