They don't teach you repacking a gland on level 2. Or at least there's no practical on it that I remember. They might mention it in passing one snoozy morning in the classroom when you're staring at the secretary.
Most of the things I now do in my capacity as a wannabe-jobbing plumber were not things we practised in college. Lot of time spent memorising British Standard numbers and trying to phathom how to assault lead into an agreeable shape but no time spent weeping over stubborn WC or taps.
I wish we'd spent some decent time on things like how to make solid fixings to crappy walls. Or showers! Never a word mentioned about showers. The whole subject still eludes me. All I know I've worked out myself by interrogating them in dark bathrooms while the customer isn't looking.