Troy Deeney's ninth goal of the season earned a point for Watford, who had substitute Adrian Mariappa sent off.
Hull started superbly when Andy Dawson's fine cross from the right was headed in by James Chester.
But the Hornets soon levelled when John Eustace slipped the ball inside on the left edge of the penalty area and Deeney turned it home from six yards.
Hull's Corry Evans hit the bar and Mariappa, who came on at half-time, saw red for two bookings in four minutes.
The point did little for either side, both of whom remain some way from the play-off places.
Following the two early goals, Watford goalkeeper Tomas Kuszczak, on loan from Manchester United, kept out Chester's header from a Dawson corner and also blocked a Matty Fryatt strike.
Evans saw an angled drive from inside the area strike the woodwork, while Josh King was narrowly off target with a header from Robert Koren's cross.
Watford defender Carl Dickinson twice went close to putting his side in front with a header and then a shot wide in as many minutes.
Hull sensed victory but Koren fired just wide from the edge of the area and then had a shot blocked.
Hornets manager Sean Dyche sent on Chris Iwelumo with seven minutes remaining and within 60 seconds the striker lashed a low shot inches wide, but the game ended in stalemate.