Legal Question in Real Estate Law in California

As a matter of law, discharging anything from your property onto a neighbor's property is a nuisance. On the other hand there needs to be some appreciable harm from a nuisance before it will give rise to a successful court case. In my experience as a homeowner, your technician is correct that there is no way to trap all the lint, but that also doesn't get you off the hook if discharge is sufficient to be enough of a problem to qualify for a court case. You may need to re-route your vent, either internally or externally to discharge onto your own property. Whether you have to do that, and whether the neighbor has a case to force you to do that, is impossible to tell over the internet.