there are trained, experienced, reliable and competent plumbers in thailand, the knack is sorting the wheat from the chaff. this would be fairly easy back home, but potentially more difficult here, depending on your awareness of thai language and culture. though, as a local, your thai partner really should be able to find an appropriate tradesman/woman. i mean, if you were back home and needed a plumber you would't expect your thai partner to find one, you'd do it yourself because the understand what's going on!