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Sink backwash?

2K views 11 replies 7 participants last post by  fallard 
#1 ·
I was about to replace the hoses on the head and galley sink and noticed that the PO used a one way flapper valve in both drains. I presume the PO used this valve to prevent water from splashing up ("errupting") through the sink while sailing in sloppy conditions.

On my boat the thru-hull is directly below each sink, its a straight shot. The sink is about 3 ft above the waterline when the boat is level.


I'm wondering:
- Is this "a thing"? will sea water actually erupt and spray through the sink when crashing through chop?
- Is some means of preventing this gusher, common? or do you just shut the seacock?
- Any downside to this flapper valve?
 
#4 ·
My Bristol 31.1 had a one-way valve in the head sink drain, but not in the galley. However, the galley had new hose just before I bought the boat, so they might have thrown away the valve. That is exactly what I just did with the valve in the head drain - throw it away. Now it is a straight shot.

The fittings at the bottom of both sinks had corroded away. Both sinks have zinc-plated nuts holding on tubular chromed-brass parts. The nut was corroded inside where you can't see it, and the tube was corroded too. A few hard pulls and the whole thing just fell apart.

Beware, this could sink (no pun intended) your boat.
 
#3 · (Edited)
All my sink drain lines have bronze swing check valves to prevent 'eruptions' in very-stink conditions.

The downside is they do foul and block easily with cooking debris, soap scum and especially 'grease' from cooking.
So we need to keep some potent drain cleaner and a 'plumbers helper' handy. We cook when underway on distance passages, etc.; and, nothing defeats cooking while underway than by having a 'gusher' spray all over the galley. A few strokes with a small 'plumbers helper usually quickly removes the occasional blockages at the check valves.
A monthly 'soak' with a strong caustic' detergent usually will keep the check valves clear; but, not always.

Ultimately closing the valve regularly will keep the valve (ball or 'cone') from permanently freezing in place.
 
#5 ·
The rubber flappers incorporated into the basin drain fittings are the way to go. They are easy to keep clean. Seawater, or worse, whatever you just drained out can certainly erupt out of the sink in rough seas. Closing the seacock is not a practical option.
 
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#10 ·
Mark, I bought a Raritan check valve for our shower sump. It's 3/4". I don't know if they make a bigger one, but it is a far superior design and can be cleaned out. Check with Raritan first. Good luck.
 
#8 ·
Mine look just like Defender 502259. However there is no mention of the flapper so a phone call might be needed. The rivet in the middle is a clue that there is a rubber disc in there.....perhaps.
 
#12 ·
I picked up a SS sink drain fitting at a True Value hardware store that fits my galley sink. This one has a built-in wing nut that screws the stopper down and prevents and "eruptions".

Otherwise I would shut off the thru-hull, as I would for the head sink.
 
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