I have put in two Racor LG-100s. I've got two fuel tanks and here is how I plumbed their vents: | | +-+ +-+ |L| |L| |g| |g| |1| |1| |0| |0| |0| |0| +-- +-- | | +---Vent Line---+ | | +---+ +---+ | | | | | T | | T | | A | | A | | N | | N | | K | | K | | | | | +---+ +---+ Note that the Vent Line is ABOVE the tanks and BELOW the LG-100s. The idea is that while filling a tank if it overflows then the fuel will run to the opposite tank through the vent line. This also has the added advantage that if an LG-100 gets stuck then the other one will take over. The disadvantage is that it doesn't "gurgle" very much when filling. It will only gurgle loudly when both tanks are full.I also agree with another post about the 90-95% fill-up. You should be able to estimate how much fuel to take on before you start and use the vent traps to handle mistakes. Ideally they would never be needed. Also, IMHO, sensors, alarms, whistles, etc are of less value. I'd rather PREVENT the spill than be told I now have one to clean up. Another possibility is to have a single vent and LG-100 shared with both tanks. I don't like this, but I don't know why not. bob M/V Lindy