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Kitchen sink outlet too low for gravity drainage


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Hi.

What are the options here? I thought poss small tank with whale gulper but not suitable?

Someone mentioned using a

Saniflow system with macerator?

Anyone else come up with this problem?

 

Thanks

 

Is there any chance that the sink could be raised, or alternatively fit a shallower sink?

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Remembering you don't need a trap on the sink

 

Richard

That was the trap I fell into.

By not using a trap (which as you say isn't needed anyway) I was able to get the level higher hence no problem.

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Are you sure the outlet is too low? The RCD says 25cm for outlet above the waterline, but you can get by this by using marine-grade hose and double clipping. The top of the sink then effectively becomes the height of the outlet.

 

ETA: And you shouldn't use pushfit or solvent-welded conventional sink waste fittings if you want to do it this way. Far easier to fit flexible pipe directly from skin fitting to sink waste attachment anyway.

 

067Sink Finished S

Edited by dor
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Are you sure the outlet is too low? The RCD says 25cm for outlet above the waterline, but you can get by this by using marine-grade hose and double clipping. The top of the sink then effectively becomes the height of the outlet.

 

And you end up with a "U" full of dirty, smelly, greasy water.

Not too bad for a liveaboard with the sink in daily use, but if a leisure boat, left for weeks between usage it can become unpleasant.

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And you end up with a "U" full of dirty, smelly, greasy water.

Not too bad for a liveaboard with the sink in daily use, but if a leisure boat, left for weeks between usage it can become unpleasant.

I don't quite follow?

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I would agree that you remove the trap, some that come with sinks these days are really low in the cupboard once fitted.

 

mine is only just enough to drain off out the side, but as per the other post my worktops are higher than normal, if they we're not then I think I would have had problems.

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Another option: http://www.toolstation.com/shop/p87482?searchstr=sink%20trap

 

But I don't understand this bit: The top of the sink then effectively becomes the height of the outlet.

 

This is as explained to me by the surveyor who oversaw my build, and he mostly does proper marine stuff.

 

Because the whole of the plumbing is of acceptable marine standard and it is assumed it can't get swamped, as water would have to rise to above the level of the sink. If using standard PVC pipe then it could fracture, and if the outlet was close to the waterline, water could come in if the boat listed or some other reason for the sink fitting to be very close to, or temporarily, under the outside water level.

 

I wouldn't use PVC pipe, solvent-welded or push fit, for a boat's waste pipes anyway, and certainly not a trap.

 

ETA: The more pedantic might say that the screwed fitting connecting the pipe to the sink could also fracture, but that doesn't seem to have occurred to the surveyor.

Edited by dor
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We had this problem on Batavia (which sits very low in the water), and solved it using a Whale Gulper pump. This works fine, with a few provisos:

 

  1. It is probably best to have the pump below the level of the bottom of the sink - ours is about 300 mm below the sink.
  2. Have a length of hose (about 1.2 metres in our case) before the pump, so that if some idiot pours a small amount of boiling water down the sink, it doesn't immediately reach the pump. Having said that, we haven't had any problems with draining pans of vegetables, etc.
  3. Ensure that the waste from the sink to the pump has a high level vented connection - e.g. the sink's overflow. A friend had a sink (with no overflow) which used a Gulper pump and all was well until someone ran the pump with the plug in the sink. The pump pulled the plug well and truly home and much dismantling had to be done to remove the plug. In any case, you don't really need a plug, as once the hose to the pump is full of water, the sink won't drain until you run the pump.

Chris G

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Some great suggestions here thanks!

I need to take a proper measurement to see where waterline is. If I do away with waste trap I may be able to get it to 180mm above waterline.

If I can do this how about then fitting an isolation ball valve just before the skin fitting in case the boat ever goes to sea?

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