Leaks in the plumbing are sometimes hard to detect because they don't leak until under boost and that is hard to produce without a lot of engine noise that covers up the noise of the leak.

I use a master cylinder cap fitted with a schrader valve to flush my brake systems using a bicycle pump. I found that the master cylinder cap is just the right size to fit into the hose that attaches to the turbo. I insert the cap in the hose and clamp it with a large hose clamp to seal around the cap. I then set my air compressor regulator to 15 lbs and pressurize the turbo plumbing via the schrader valve. Any leak is easy to hear.

My experience with a bad hose also produced a rich mixture with black smoke out the exhaust.

Randy