I went to MTT last month. Got the 10 baht bus No.166 from Victory Monument. It dropped me at the front door of Chiang Watthana. From there I got 60 baht taxi ride to front door of MTT.
I actually got on the wrong bus, there’s two no. 166 busses. Anyway it was cheap and easy. I was in and out just over 30 mins. There’s a chap on UTube I followed for these directions. Just type in how to get to Immigration at Muang Thong Thani. Very informative man.