Our fuel tanks are fitted with a metal dip stick which screws in at the top of the tanks. (MT 44). When taking on fuel I remove the dip stick and this gives enough venting to prevent the problem discussed. The access to the top of the fuel tanks are easy on our boat as I just have to lift the seat lid on the settee (starboard tank) and remove one chair over the sole hatch (port tank). Of course this may not be conveinient in other boat styles. For many years our vents were suitable when marina fuel pumps did not refill at fast speeds. Now with the newer faster pumps at marinas I have resorted to the above which saved me from having to repipe new bigger vent lines. Leonard Stern MTOA#893