Ice box drain and antisiphon valve problem Thank you

[Tom Madden]

i have a 2007 catalina 34ft mk II, hull number 1768.

i've began experiencing a problem where water spurts out of the top of the antisiphon valve when i use my ice box drain sump pump.  my ice box drain systems seems clear (no clogs) and the sump pump seems to be working correct.  when draining the ice box, i close the valve from the shower pump. 

the outgoing drain water seems to be getting backed up in the outgoing hose between the antisiphon valve and ice box drain outlet through hull seaacock.   have double checked to make sure the ice box through hull seacock is in the open position.  i've also disconnected the hose on the outgoing side of the antisiphon valve and have blown into it.  i can blow the water out and can even hear the bubbles i'm creating under my boat as i blow (no comments please.)  however, after i blow the water out it seems that water comes rushing back in through the seacock (i can taste it and its sea water.)  so, i'm not sure if the sea cock is to work this or if this might be my problem.

hopefully i've described the problem clearly.  i appreciate any input very much.  thank you in advance.

tom madden
i want to thank every one for their input.  my problem turned out to be the check valve (small rubber piece) inside the antisiphon valve.  i believe my root problem was running my ice drain sump pump without opening the  through hull seacock valve.  this caused to check valve to get forced out of the top whole ( i think, since it was missing.)  i installed a new antisiphon valve and all is well now.  many thanks to those providing input.  thank you!  tom

[Stu Jackson]

Tom, antisiphon valves need to be checked and serviced.  You should remove the top of the antisiphon loop and carefully remove the small rubber flap under the hole and clean it and its housing up.  Remember what position it was in (up and down) for replacement.  Since it's partially seawater you're dealing with, it could have been gummed up with salt.  I don't remember a good antisiphon loop description on our website, so can't link you to something right here, but they're pretty well covered in most good boating plumbing, engine and head books; read up and learn what they do, why and how.  There are a few others on your boat...

[Mike and Joanne Stimmler]

Tom,
Since you're a close neighbor, I'll try to add my two cents.
You said that when you blow through the hose, you can hear bubbles out side, which sounds like that part is clear. The water rushing back in would be normal if the level of the hose you're blowing on is below the waterline or even slightly above it since the momentum of the rushing water may push it a little further at first.
I agree with Stu and also think that the problem is with the anti-siphon valve.

Good luck,
Mike

[Ron Hill]

Tom : Why not think about installing a "one way" valve in that line !?! 

[Wayne]

Tom, you said water was squirting out the top of your anti siphon valve.  I had the exact same problem.  I forgot to open the thru hull before testing my shower sump.  The top of the anti siphon has  little black rubber one-way valve called a duck bill (because that is what it looks like).  In my case, my forgetting to open the seacock 'blew' the duckbill out of the top of the anti siphon when I turned my pump on.  Is the top of your valve flat with a hole in its middle?  That hole is where the 'duck bill' belongs, bill side up.  Inexpensive item and WM.