I used to pump around 180ml each session...but I become tired and got the flu one time so I skipped a lot of pumping session then now my milk supply dropped. try to be dilligent about pumping, and yes its very exhausting. maybe buy pumping wipes so you can just do a quick wipedown after pumping instead of washing then its not as bad.
Used to pump around 800 per day. But my milk supply has dropped to 400-500 per day.