Head anti-siphon - to prevent sea water flooding

kable · March 12, 2018, 07:37:57 PM

So I close all my seacocks when I leave the boat, when moored at my home port. So I haven't been too concerned with this.

A year ago, my son accidentally left the wet/dry switch in the wrong position and the bowl overflowed. Did a bit of research and realized "the owner" is suppose to add an anti-siphon between the head's pump and the bowl by removing the factory supplied small white hose on the toilet.

Has anyone actually done this? How did you do it without it looking terrible?

http://www.xylemflowcontrol.com/files/29090_29120-3000_43000-0905.pdf
Section 5.2 of the install manual.

Thanks,
Kable

(obviously the spring bug has bitten me and I am looking at all my boat work/learning ahead)

Stu Jackson · March 12, 2018, 08:25:34 PM

While it requires additional holes in the bulkhead, mine is located at the outboard end of our nav station hanging locker. Or you can leave it exposed, which is MUCH easier to service.

Your boat, your choice.

Noah · March 12, 2018, 09:19:55 PM

Mine comes up inside the port cockpit locker up against the back of the head bulkhead. Bad photo attached.

Bill Shreeves · March 13, 2018, 09:03:23 AM

Kable - I have the vented loop as shown in diagram 1 in your attachment and it's located in the hanging locker like Stu's. I can't leave the valve on my Groco head on the wet side or the bowl very slowly fills and has since I bought the boat in 2016. I'm still just a couple seasons in and new to this. I know the vent for the bowl supply water is fairly low and close to the outboard side in the locker so, maybe that is why or the vent needs service? A project I will am beginning in next couple of weeks is to replace all head supply and waste hoses, clamps and move / service the vents etc. I plan on moving the vent as high and close to mid ship in the locker as I can.

kable · March 13, 2018, 06:40:30 PM

Thanks for the great replies.

Any photos from the toilet side would be appreciated? I guess in my mind the hoses had to go UP, but I guess they have to at some point. They can first go sideway through the wall, then up.

Thanks,
Kable

Dave Spencer · March 13, 2018, 07:36:43 PM

Kable,
Only true boat lovers take pictures of their toilet! And I have several.

My vented loop goes through the liner behind the toilet and then up to the medicine cabinet. The nipple on the vented loop is easily accessible to service through the medicine cabinet. The hole through the liner is almost always hidden by the shower curtain that is drawn across the medicine cabinet when showering. Here's a picture from the toilet side. The hole in the liner is mostly obscured by the shower curtain but you can see part of the black grommet on the hole through the liner. Hopefully you get the idea. Unfortunately, I don't have any pictures inside the medicine cabinet showing how the vented loop is mounted.

kable · March 13, 2018, 10:23:05 PM

Thanks!

Jon W · March 15, 2018, 02:13:49 PM

Two views of my anti siphon. They say beauty is in the eye of the beholder, but I like the way this came out. Access is easy, the anti siphon is at deck height, and no holes in the boat other than two small screw holes to fasten the anti siphon valve. If you go a similar route, be aware that bulkhead between the head and Nav station is very thin.

kable · March 15, 2018, 07:37:23 PM

Thanks, looks pretty straightforward.

John Langford · March 23, 2018, 10:33:13 AM

And, BTW, access is important because it is so easy to lose or improperly reassemble the duck bill and cap when checking it. I speak from experience. MKII owners who have to deal with the engine vented loop underneath the head sink will know what I mean. My duck bill once ended up upside down so that running the engine after caused significant spouting from the top of the evented loop.

Jon W · March 23, 2018, 12:26:42 PM

What is the engine vented loop for and why on MK II but not on MK I's? Thanks for the help.

John Langford · March 25, 2018, 01:47:29 PM

Jon
I can't answer the second part of your question but the first part is easily researched. See for example:
https://www.cruisingworld.com/how/simple-valve-prevents-flooding

Jon W · March 25, 2018, 03:47:33 PM

Thanks for the link. I'll double check tomorrow, but pretty sure there isn't a vented loop between the raw water pump and the exhaust riser. Another project for the list.

Jon W · March 26, 2018, 05:32:26 PM

Guess I need to correct my statement. Took a look today and I do have an engine vented loop. I suppose it could be mounted higher, but it is above the water line.

Bill Shreeves · May 30, 2018, 07:33:26 PM

Quote from: Bill Shreeves on March 13, 2018, 09:03:23 AM
Kable - I have the vented loop as shown in diagram 1 in your attachment and it's located in the hanging locker like Stu's. I can't leave the valve on my Groco head on the wet side or the bowl very slowly fills and has since I bought the boat in 2016. I'm still just a couple seasons in and new to this. I know the vent for the bowl supply water is fairly low and close to the outboard side in the locker so, maybe that is why or the vent needs service? A project I will am beginning in next couple of weeks is to replace all head supply and waste hoses, clamps and move / service the vents etc. I plan on moving the vent as high and close to mid ship in the locker as I can.

So, I finally got around to the work. In the process I learned two new things and reinforced another. After marking out the static water level on the nav station hanging locker aft bulkhead I saw that the vented loop in the locker was 8-10" above the waterline however, the duckbill rubber vent was actually a solid piece of rubber that couldn't prevent siphoning. Just another example not to trust anything I inherited from the previous owner.

-Bill