My Daughter had this exact procedure for an abscess on her small intestine in 2008.
She had the drain in for 10 days. Also, irrigated 2-3 times a day. I seem to remember a small amount seeping on the surface where the drain went in, and seem to recall that this was normal.
Once the drain line was removed, it closed up pretty quickly. She was also on Prednisone and Flagyl for some time afterwards to make sure the sac didn't refill.