Can someone tell me what the benefit to blowing out with a pressure washer is and how it is done correctly. Never had to do it, just curious.

The benefit of using water to clean out whether at high pressure or low pressure is that there is virtually no energy stored, as water is 'incompressible'. High pressure water (over a couple hundred psi) is not necessary or desirable for a normal clean-out, because of the low water volume that high pressure pumps normally put out. What high pressure water is used for is to clean out green or hardened concrete from pipe system after a boom party. Care must be taken as well, like monitoring the pressure delivered, and having a way to safely relieve the pressure. Generally one would use high pressure to clean green or hardened concrete out of one section of pipe at a time. With high pressure there is the potential to push out the lining of twin wall pipes. A high-pressure water pump, such as a pressure washer, can put out 2 or 3 times the pressure that the concrete pump can, and the pipe system's rating as well. Have I explained this well enough? If you have a specific question, fire away!!

I've blown out with water many times, what I was referring to was hard concrete or a boom party, we have always used air and nobody likes it, I've heard of using a pressure washer but I've never worked with any one that has done it and didn't know if it was worth trying, Thanks for the help

You have way more control over the rate of 'push'. Volume of water in = volume of concrete out. It pressures up, the concrete moves, pressure drops to nearly nothing instantly. you also have more pressure available. And no 'explosion' at the end. If there is no entrapped air at the water attachment point, it's pretty anticlimactic when the last bit of concrete exits the pipe.

I like anti climatic!

 Besides the violence and danger involved. There's alot smaller window when trying to save pipe with air pressure.

 The right pressure washer can blow out a piece of pipe (fence post) that's been laying behind the shop since the day of the party. Whether it was last week or last summer! 

 It's sometimes even powerful enough to push the interior sleeve out on dual wall pipe!

Is that hose pressure hose at the bottom center? Will a home depot cheapy work with 2300psi and 2 or 3 gal/min.?

You bet, the Home Depot cheapie will work!

You could do it with a grease gun, even, I think a grease gun would pump priming gel. Got the time? Go for it.

Thanks guys!