Okay to run engines off flat hoses?
 

Okay I have some nice new flat, easy coil hoses but I am very nervous about flushing the engines via perko flush kits with them, as I am worried the thin walls of the hoses may be sucked together. Hence, I have not done so. Anyone have any experience with this?

I have no experience with them, but can't you flush with the kits without running the motors?

I have done it - You should not have a problem. The pressure from most hose outlets should more than offset the draw of your engines. The water will keep flowing.
Run a test with the engines at idle. Once the engine fires up feel the hose, there should still be pressure in it.

The only time you would have a problem would be with a low pressure/low flow hose outlet. (You would also have a problem with a regular hose in that situation.)

Great Stevel that is the answer I was seeking! Many thanks!