The Collaborative International Dictionary
Flip dog
Flip \Flip\ (fl[i^]p), n. [Cf. Prov. E. flip nimble, flippant, also, a slight blow. Cf. Flippant.] A mixture of beer, spirit, etc., stirred and heated by a hot iron.
Flip dog, an iron used, when heated, to warm flip.
Wiktionary
flip dog
n. (context archaic English) A heated iron used to warm flip (the drink).