To figure the house advantage on doey-don't, multiply 1.41 X 2.
The house edge for pass / don't pass bettor (assuming equal bet amounts) cannot be 1.41 x 2 -- that makes no sense.
A quick approximation is 1 bet out of 72 bets since you lose 1 bet, on average, in 36 rolls but since you are making 2 opposing bets at the same time, the edge is 1 in 72 bets as a guesstimate.
35 times (or 70 bets) that are non-box cars are a wash or net to zero. One bet wins, the other bet loses. It's the box car where one bet loses and one bet pushes, thus losing one bet in 72 bets.