Rubber trees are a really popular crop around Củ chi, an hour or so out of Ho Chi Minh City. After leaving the tunnels, we stopped and wandered around the plantation. We met one of the workers who was happy to have his photo taken.
They score the tree and the rubber sap drips into the coconut shell.
I believe they score the tree about every 2 weeks. This gives it a little time to heal.
Here's a little animation Google Photos did for me.