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What year is your coach and what chassis is it built on ?
That amount pressure drop in that short a time is a major leak and has to be delt with .
Your air pressure system should also build faster than 10 mins .
Slow build time indicates the leak is close to the compressor's capacity .
One tank supplies the front brakes , the other the rear .
Air pressure supply to the suspension from which tank is dependent on the chassis manufacturer.