Outside of IAH Terminal B Gates for B1-B10 (which won't let you enter more than 30 min prior to your flight), you'll find restrooms. Inside if you veer to the right side and look on the left row of stalls, you'll see a large stall that was converted into a pump/nursing area. 

It was fairly clean - contains a sink with soap and paper towels, room to move around, ELECTRICAL, and a wall-mounted seat for an infant or small child to be strapped securely. There is no toliet(!). 

Not 100% great (cracked tile, lots of "bathroom noises" from surrounding stalls), but it did the trick and was better than nothing. Wish they had a chair in there, but just thankful there was no toliet!