Putting in a new bathroom in the upstairs. When putting in the tub and drain, is it necessary to cut a hole in the ceiling below to connect the new drain upstairs. Please help.

It depends how you have set up your rough-in. If done properly than you should be able to connect drain through service door behind the tub. Otherwise, you will have to cut access in the ceiling down below.

If plumbing is installed with floors opened upstairs then you could prefab waste and overflow before setting tub by taking your center demensions. As an apprentice you would probably open up ceiling anyway. So basically I wouldn't use a panel.

In my area of operation, access door is required. Usually, the door is behind the tub. In some cases, it may be in the ceiling in the garage.

Milo,
I didn't say it is illegal. That is just the way I do my work without opening walls or ceilings if I don't have to. Thanks