how do they get the pip out?

We are driving along in the car, on our way to something or other. Gaye is driving, I am in the passenger seat, Thomas is in the back. We are talking about where we are going and what we are looking forward to about it. Then...

"Hey Mum..."
"Yes darling?"
"You know those men, the ones who help people who don't have pips... how do they get the pip out?"
"Sorry darling?" Confused look from me to Gaye
"You know those men, the nice ones who help the ladies who don't have a Daddy to have a baby - how do they get the pip out?"
"Ohh you mean the seed, when a man donates a seed so someone can have a baby?"
"Yeah, how do they get that pip out of their pe*is"
(At this point I admit I couldn't hold it together, I got all giggly thinking of blokes and p**n in a small room at a clinic. I mean I really do try to be factual and straight forward with him about such things, but I was a bit confronted about this. I am ashamed to say that I fell on the when you grow up sword....)
"Darling it is kind of a grown up thing, the sort of thing that you learn as you grow up."
"Just tell me Mum, I don't care if it is a grown up thing, I want to know the truth"
"It is hard to explain really, you know how you just know how to do a wee? Well you will just know how to do this when you grow up"
"Does it hurt"
"Not even a bit, you just know you want to and so it comes out"
"Really, I get it. So you think about it and make it happen"
(We jumped on that boat let me tell you)
"Yes, that is it completely. When you are grown up your body will tell you how to make it happen and then you will be able to"
"Ahh right I totally get it"