>Breaking vacuum could be as simple as flattening a >silicon rubber tube. Or
you could have a simple on / off >valve in the handpiece - or perhaps a
"vent to >atmosphere" that shunted vacuum away from the needle >tip.

Try a hole in the side of the tubing. Place finger over tube to create
suction, remove finger to relieve suction. Works in the medical profession
(making an impromtu ventilator from some tubing and an O2 supply except then
it is the other way round ie +ve pressure!).......
Also if gunging of the needle is a problem- couldn't a switch be used to
blow air down the needle instead of sucking up it. Maybe a foot pedal. Blow
out all the goo??

Ben

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