Th sounding like a 'd' in dog or a soft 'v' sound like move. Both are incorrect pronunciations. Th should sound like neither. A harder sound of a c or a z in Penisular Spanish might be closer. Listen to a Spaniard say "Hacer" and the 'c' sound is very close. Sorry hard to explain how to make a sound.

Tem que colocar a lingua entre os dentes para fazer o /th/ de that. Não pode colocar a lingua atras dos dentes (como /d/), e não se usa o labio inferior (como /v/) para pronunciar o som de /th/. Pode ver como se faça e ouvir o som no sitio web: http://www.uiowa.edu/~acadtech/phonetics/english/frameset.html. Clica PLACE > LINGUA-DENTAL

Neither one is correct. Sometimes you will hear "dat" in slang conversations or improper English. For example: Gimme dat book. But usually the tongue is between your teeth when you pronounce the letters 'th' together.