Any plumbing pros that can answer crazy plumbing question?

[Mike Palmer]

I have a unit that has experienced way too many plumbing issues. Now it seems I have a toilet that has some issues. For one it doesn't seem to flush very well. The tenants have not complained, but I have noticed that it flushes very slow, has no 'power' to the flush, and you sometimes need to flush multiple times to get it to go down if there is anything but liquid in it.

Well then the other day the tenant sends me some pictures of the toilet filling up with soap bubbles. It seems that when the tenants upstairs take a bubble bath, that bubbles come up into the toilet bowl and up around the bolts and around/through the floor area. I have tried to attach pictures, but the bubbles basically come up from under the floor and up through the toilet. The bubbles on the floor came up through the floor (they did not overflow from the bowl onto the floor).

Does this indicate that the toilet is not installed properly? Or that the toilet needs replaced? Or is there a problem farther down the line? The bathtub in this bathroom was recently plugged but some draino took care of that. Apparently this soap bubble issue happened previously about 4-6 months ago, but they asked the upstairs tenants and found out they had taken a bubble bath and so they didn't worry about it until they saw it happen again this time. What would make the soap bubbles from upstairs come up through the toilet???