Most tear staining that I am familiar with comes from food dyes or seasonal allergies...or both. The Tylan works well and may last for weeks or months. It is good as a treatment until you can determine the cause. If the cause cannot be determined then you may have to pulse it every so often once it's under control. Every dog is different and will require different treatments...so a measure of trial and error should be expected.
Our youngest, Lala, started showing stains at 6 months. We were pretty sure it wasn't the NOW food so we assumed it was seasonal allergy. Treatment with tylon cleared it up in 10 days (the staining never got bad). That was 7 months ago. I'm hoping it doesn't return next spring but if it does I'll know what to do.