I've never had one. Had plenty of negative pregnancy tests but never an evap line, both times I had pos pregnancy tests they were very positive straight away, this time there was no line within 30-60 seconds so I chucked it in a drawer and forgot about it. 3-4 hours later there is a definite, thin line (not as thick as I think an obvious strong positive would be but there all the same.) Sound like an evap line?