I am new to the site. a lot of great info. I have been reading about Jabsco heads not pulling in sea water to flush. I am having this issue as well. I have already replaced the pump assembly. this did not help. I checked the sea cock and water flows fine from there when I pull the hose off. the head flushes fine dry. it all goes to the holding tank. I am guessing maybe the vent is clogged? any help would be appreciated.