Apparently ESP is 5v tolerant, at least according to CEO Mr Teo Swee Ann. That said, 2.2k resister on echo is a good idea if you don’t have a HC-SR04+
More… https://www.ba0sh1.com/blog/2016/08/03/is-esp8266-io-really-5v-tolerant/
I’m in the process of building a hobo twin sensor right now using one wire hack (and newping)… will report on results.