Lokissimo
Citizen of Zooville
It depends on many factors: the size of the knot, the depth of the tie, how prepared you are, how excited you are... plus a million small details. However, in my experience there is always some element of pain involved. For me, the pleasure usually outweighs the pain by a great deal.This has always been a curiosity for me. When you get knotted does it hurt and is the dog constantly pumping semen in you?
As for the second part of your question, the dog usually ejaculates most of the time but most of the time it's just precum. The pumping and throbbing is really pleasant and I personally love the volume of ejaculate they can fill you up with.