Stripping can mean removing cash, products, people and/or weapons.
Cash, send cash to some other country with the "my Empire" link. Use the same link for transferring offensive, defensive and strategic weapons. Cash will always be taken when someone is done stripping a country. Usually weapons too.
Products can be sold with direct sales. Personally I prefer dropping the trade strategy and eventually turning off the automatic purchases. After making direct sales transfer the cash. This can be tedious. I would suggest skipping things like 6 months of potatoes. Four production plants at 15B each might be worth clicking the mouse a few times.
If the population is over 30M you can send 1M per month to the rest of your empire. When population is over 20M you can sell workers on the open market.
You can also exchange workers. You can trade 400,000 per month but only move a maximum of 200,000. If your con