After I ate meat, can I use a dairy plastic cup to drink from? The cup has had dairy in it, not just that its used during dairy meals, and it is cleaned with hot water.
If the cup was washed out and it is clean of milky residue it is permitted to drink from it, after eating meat. Technically it would be permitted even during a meat meal, however for practical reasons it is not adviseable, because things can get mixed up.
Badei Hashulchan 8-27.