While I understand that pumping “feels obscene” to you I don’t think it should. I once stumbled in on a co-worker who was using an empty conference room to pump. Nothing was exposed, so I had no idea what she was doing, and wouldn’t have known if I hadn’t asked if I was interrupting something. She smiled and said “Pumping”.
It took me a few seconds to catch on, but I now regret the look of horror that passed over my face. I wanted to explain that I was upset with myself for walking in on her, not because she was doing anything wrong, but I felt I’d already imposed on her privacy enough at that point. Hopefully I made her laugh and helped break up the tedium.