We used black swan in the tub last night to unclog our drain, it wasn't clogged it just took forever to drain. My husband is in building maintenance and has used black swan before. The tub is now completely backed up, but our toilet and sinks work fine. I live in a 36 unit apartment building. Help! What can we do to alleviate the clog!!

Do what a "building maintenance" person should do in the first place, and snake the drain. Chemicals are SELDOM effective to unplug a drain, and even when they do work it is only for a short time.

you can cover the overflow with an old towel and try plunging the drain.
be careful as there is a chemical cleaner in the water..

It wasnt plugged up in the first place, we were trying to get the drain to drain faster. We have used black swan before with no problems.

If it is a tub drain restriction, the cause is usually hair, shampoo, softener, conditioner and soap grease. Since you are apartment dwellers, its the apartment management's responsibility to clear n clean the waste lines. If you cause damage to the line or tub surface, you could be held responsible.
Best Wishes