Rather than blowing out the pipes, which still may not prevent the occasional drop of water from spoiling the job, after gravity-draining the line, I take some bread and stuff it into the pipe, enough for a 1/2" or so thick plug inserted an inch or two into the pipe, just before sweating the joint. The bread will rapidly disolve and pass through the system when it is repressurized and bled. Just be sure to remove faucet aerators when bleeding the system or they'll get clogged. I also have the toilet and water heater supplies shut to keep the bread residue out of them.

I know this is the diy way, but we had to replace our plumbing after all of the copper was stolen while the house was vacant. What complicated the matter was that the pipes had been cut off with a bolt cutter right at ceiling height. Attempting to solder was too dangerous as we still had to get a clean cut, so at that point we were reaching up through the walls just to cut the pipe - we used SharkBites (I think from HD, maybe Lowes) and they were fantastic. No problems after 2 years :)

randy427 - thanks for the tip. My pipes are run in the slab on a single story. I think gravity would just end up leaving water in the pipes where I need to solder about 2" or so above the slab. IE: I think the pipes in the slab are at the lowest point so how can gravity possibly work? I think I will do the air compressor and the bread tricks. For adding a gate valve I may as well use the jet swet since I now own one. As mentioned before, overkill is better at this point for me!

library girl - sounds painful ... I looked at those sharkbites at HD ... aside from being expensive I don't trust that they will stand the test of time like soldered copper (IE: you are 2 years in but what about 25 years?) ... maybe they will just leery of plastic in general.

If you are working on a potable water line, a straw or small diameter vinyl hose can be used to suck the water out.
The air compressor will work too, but a more localized method is to use the air to run a venturi that sucks the water out.

Such a thing is easily made from a small diameter wye fitting. I have an explosion proof sealoff with 1/2" FPT but one could be easily made. Run the air through the straight and the branch becomes suction.

I ended up blowing out the air with the compressor. It got a lot of it I think but I also used the bread trick as well. One of the pipes still was wet inside and the bread dried it right up. Also ended up chopping the ends off some heater hoses and using that for flex line. They don't sell 3/4 copper flex at my home depot but do sell the copper heater connection hoses. Anyhow, no leaks now and all is good! Thanks for all the responses, really helped me out!

Heater hose?
I don't know of any that is rated for domestic water supply pressures or for use in potable water systems.

The heater hose I'm referring to is the copper flex type used to make the connection to a water heater. It would be under the exact same pressure as the cold water input side to the water heater. In my case the pressure regulator is stuck at ~70 PSI. Is this a no-no? I've sealed up the wall and called it a day. Hopefully it survives!

Here is a picture of the work:

ttp://tinyurl.com/6q9yur7

http://tinyurl.com/6q9yur7

OK, not what I was thinking when I read 'heater hose'.
Some local codes no longer permit these flex-lines to be used for water heaters, either.
In any case, they should not be sealed up behind a finished wall. The flex-line walls are thinner than that of tubing, and more prone to developing leaks over time so they must be readily visible for casual observation.

Water heater hose... here's a wiser choice... http://www.falconstainless.com/index.html

I don't believe those are rated for in-wall installation, either.

Nope, not in-wall. If you are in-wall then you need to do it right or learn how to repair sheet rock.

Thanks Guys.

It's really tight in that area so if I were to open up the wall again could I use the solid type of flexible copper that is not corrugated? Can only find long lengths being sold of the 3/4" flex copper online but not at home depot. I had disabled a water softener hookup (this is being turned into a rental home) ... but could run 3 sections of flex out thru the back of that hole and then tie them all together where I have more room.

Thanks Guys.

It's really tight in that area so if I were to open up the wall again could I use the solid type of flexible copper that is not corrugated? Can only find long lengths being sold of the 3/4" flex copper online but not at home depot. I had disabled a water softener hookup (this is being turned into a rental home) ... but could run 3 sections of flex out thru the back of that hole and then tie them all together where I have more room.