well tell the kiwi how you would do it.

In less than 10 seconds hopefully :D

One piece at a time

very carefully, depending on the location and the equipment there is a few choices I would have to know are you in the city in the woods what ? I have blown 1000' at a time had a air compressor and fittings 1 at the pump then another at the 1000 ft mark and blew them both at the same time  but we was in the middle of the swamp and our pigs were never seen again in confined areas you get 10-12 good backs and go to dumping and loading with a few guys washing I have sucked back 500' with a sponge on a tk 70 but surely you are pushing it with something alot bigger.

I use air if it can be done safely.
If not i break it down to sections and clean it out with a ball and water from the mixer truck or pump.

Air with some savy,some don't get it.

dump and wash out hopper, put ball in swing 90,close trap fill hopper with H2O,and pump it clean.mixer water,fire hydrant,any available.  

How about using air on the end of the system and suck back a pig, with the pump reversing at the same time. It should be safe as long as you have a relief valve. The company I just bought my boom pump from uses a pig and air on all their pumps. They A frame over, hook up a blow out cap and suck and blow the pig back to the hopper. Advantage? It keeps shiny clean pipes and makes the next prime a breeze.

WE are in a safe location and i am using a dive bottle with a adjustable regulator, at the moment are up to 300 meters (thats about 900') of line and its going good by the time the bottle is empty the pipe is almost empty so we just hook up the compressor for the last bit, l give it about 400' of air (the air line from bottle to pipe is a hydrolic with hydrolic conecters) to get it moving then back it off....not looking forward to another 3-400' of line...l know it will be 50% luck if we never have any probs'..and we have no water on site!!! would still like more idears....safer ones!!!

You don't need much water, about 100 litres is all you, can do it less too, 20 litres and do this two times and your lines will be clean enough to eat from.
Blow out with air, stick a ball in, blow it a bit down the line, fill with water, stick another ball and blow it out.
Clean!

as the NFL judges would say,upon further review.

Does anyone tap the pipe with a hammer anymore.I mean really,it's very simple.I trust the proper blow out cap is used.I have done so many long blow outs it becomes a natural.Once the pig/spounge gets to a certain point cut the air,nature takes over.Yeah sometimes you miss and have to hand empty a few but oh well.

yes l do all that pump NOOb l push about 50l of water to flush out. we have water but we are being watched by some "greenies" and are working over sea water...extending a wharf...and we are not allowed any dirty water into ocean...bumma. i guess we have to pay some price for living in clean green New Zealand. 

We have cleaned out 3600 feet and used a high pressure wate pump. That is the safest as water can't be compressed. Make sure you use a go-devil as well. We have also done 2500 feet with a Schwing BP750 and water.