Plumbing not draining after reassembly
Typically if drain plumbing is not done right, it will drain perfectly fine...  onto your floor.  For it not to drain, means you have a blockage.  Take the parts you fixed apart and do an inspection for any clogs.  If they are free, assume the blockage is farther down the line.  If that is the case, use a hand snake and snake out the drain before you put it back together again (make it easier).  Reassemble and see if it drains.  If it doesn't drain, try snaking again.  Typically the cost of a hand snake is cheaper than calling out a plumber.