the drain hoses are for excess fuel that is introduced into the fuel servo during the priming process.(assuming you are injected). sounds like you may be priming a little more than needed. i ran into the same issue with our new `172 versions. Cessna denied warranty because they say that the bellows in the fuel servo were damaged by overpriming. but cessna installs these drains to prevent excess build up. right. anyway. try starting her with the fuel pump on a little less and see how she runs.