Lapping valves can be frustrating as the suction lets go on the valve lapping tool, I came up with a quick fix that works well
Go to a local hardware store ( I used Wilkinsons) and buy some sticky Velcro patches
attatch one to the wooden valve lapping tool by using a very small self tapper
attach the other half to the valve itself using it's own sticky back
no more lost suction
Simples !