What is the fall from the anti-siphon valve to the thru-hull or holding tank
? (Hopefully you're not pumping out through the hull
in Cortez!) The only way the valve would leak is if there was enough pressure in the line to force the waste material up into the valve, which should ot be the case unless there is an obstruction in the thru-hull or their is an obstruction in the vent in the holding tank
. If you're using the holding tank, given your location, check your vent line. The "mud dobbers" may have made a nice little nest that is obstructing the vent. If so, It will be in the first few inches inside the thru-hull fitting. We had this problem with a vent on our Cal
2-29 when we had her at Snead Island.