I went swimming last year in just a regular 2 piece bikini no frills or anything. That was only 8 months after i had started to transition, 3 months into HRT. I had no problems at the beach with just a regular tuck, no tape. No body is really looking down there to begin with and unless you're legs are wide spread out no body is really going to see anything anyway.
I was even in Mexico for a week at New Years, so in bathing suit practically all the time, no issues had at all.