This is the job I have been putting off for about a week. Re-rigged the water manometer, pumped it up to 550mm of water head and disconsolately watched it slowly sag to near zero. I tested all fittings with a squirty bottle filled with soapy water that I use for gas connections and find a big leak where the manometer attaches to the delivery pipe. It looked airtight to me!
Re-rig the connection with a wire wrap tool I bought at Oshkosh in 2010 and had found no previous use for. Now holding pressure by eye, so walk away and wait.