TromboneChat

This is more to satisfy my curiosity, but will gladly pass along any tips to my student.
I have only owned trombones with rotary valves. I have a student with a 42 with a factory Hagman valve; he told me that when he bought it at Dillon Music the guys there went over how to maintain it. He has also watched videos online.
During a 45-minute lesson, he has to remove the bottom cap and let the valve drain several times, in addition he sometimes wipes the inside with a clean rag and gets greenish colored crud out. At his last lesson he had to also add oil because it was sticking. (It had sat for a week while he was on vacation)
Is this normal? Is there something more that he could be doing? It seems to be excessive, at least in comparison to a rotary valve.

Sounds about right.

So far I've never had to to drain them during playing other than blowing water from the slide whilst engaging the valves but do find water sitting when I remove the caps.
I do have to oil them after every time I play otherwise they go sluggish/sticky.

Bach does a very bad job at installing Hagmann valves. What you are describing is absolutely not normal. I have a tenor and a bass trombone with Hagmann valves - installed at the Hagmann shop.

They have been basically maintenance free for 20 years. Some oil once a week and I NEVER had a sticky valve.

Hagmanns vary a lot. Some stay clean, some go green. Some get sticky, others stay free. I oil my Hagmanns under the valve cap and through the tubes before every use. That gives them the best chance. They will need a strip down every so often. I've owned many sets. They blow great but are fiddly to maintain .

Never had an issue with Rath, Courtois and now Thein. Oil them! (As you should with any valve)

I use Holton Rotary Valve Oil on the valve every time I use my LT42AG. I occasionally put some Marvel Mystery Pneumatic oil (not the red stuff) on the spindle. It has never turned green, never got sticky, and has never been apart in ~25 years of service.