the breater valve will let the intake suck in air when the filter is completely under water. search "hydrolock" and read about the horror stories. the valve comes in different sizes, so find the one that matches your system. it should be about an additional $40 (on top of the cost of the intake), but it's worth it ... its either the valve, or a new engine.

when you read the stories ... they always begin with "well, it happened ... i though it would never happen to me, but ..."

you need to attach the valve along the pipe, but too close to the throtle body. to install, you need to cut your pipe in half.