Is it normal to have swelling at the area where the drain tubes (sides) are located and how long does the swelling last?

That is a great question.  I typically bring the abdominoplasty drains out through 2 small incisions in the mons area.  With or without drains, swelling after surgery will increase for the first three days and then slowly diminish.  There may be even more temporarly swelling if wetting solution was used and if you are wearing a binder that doesn't include this area.  The swelling then decreases-much is gone by 6 weeks but some subtle swelling can last for 4-6 months, and the lowest, most "dependent" areas take the longest to resolve.  So swelling in the mons area is expected.