Can dishwasher waste flood the kitchen?

[Kes]

Hi,

I am just fitting my extensive and expensive kitchen new units. The sink has been moved and the new sink waste is too high to fit a dishwasher adapter before the sink trap, so it's a stand pipe (at around the minimum height of 280 mm). It's inside the unit holding the sink, no surprise there.

Now I have a vivid imagination (or, I worry a lot). What happens if the waste gets blocked somewhere downstream and the dishwasher empties? Does the standpipe overflow and the dishwasher continue merrily to pump hot water into the kitchen cabinets? Will all my work (and the cabinets) be ruined? Would it be better if I rigged some sort of adapter (like the hated B&Q in-line adapter) so that there's no open end to the waste pipe?

Rgds.

 

[JohnD]

Why is the stand pipe so low?

I suppose you could have a separate waste pipe to the soil stack if you wanted to.

Or you could put a big bowl under the stand pipe.

It does have to have a vent.

 

[Kes]

Hi,

Why is the stand pipe so low?

Because the waste from the sink trap goes straight (or slightly inclined) out of the back of the units, and 280 mm is the difference between the waste pipe and the underneath of the worktop, so it's actually so high.

I suppose you could have a separate waste pipe to the soil stack if you wanted to.

No chance. Physical difficuilties, and it would still be at the same height as the existing pipe.

Or you could put a big bowl under the stand pipe.

So the answer is that the dishwasher will continue to pump if the waste is blocked. This could happen whatever the height of the standpipe/waste, to anyone.

It does have to have a vent.

The B&Q pipe adapters don't, as they fit into the waste pipe downstream of the trap. Or are they meant only to be used to tap into an existing standpipe for a washing machine?

Rgds.

 

[breezer]

What happens if the waste gets blocked somewhere downstream and the dishwasher empties? Does the standpipe overflow and the dishwasher continue merrily to pump hot water into the kitchen cabinets?

yes it does.

I have seen it happen twice when i used to work for HP.

one time the call was m/c leaking, it was a blocked standpipe and on rinse pipe filled up and over came the water (it ran under the kithcen units and under from the front of the m/c

2nd time was m/c flooding, cant be stand pipe because customer has cleaned it

I pulled stand pipe out (push fit) held it upi t the light, gave it to the customer and asked if its clean why cant i see light at the other end?
Customer appologied profusly there for all to see was, well a blockage

 

[ChrisR]

You CAN plumb the hose to a spigot, with a jubilee clip over it, as long as there's an air admittance valve somewhere. These can be in-line "antisiphon" valves, or fittings which go onto the 40mm plumbing. Then if the waste blocks, the pump is pumping into a blocked end.

My DW and WM have got grilles and traps in the floor underneath them both. Machines spring leaks without the wastes blocking.

 

[Agile]

Although its technically incorrect without an air admittance valve, which acts as an antisiphon device, even using your B&Q fitting has risks.

If you leave the machine washing and the waste got blocked then it would just pump out into the sink until it overflowed onto the floor!!!

Tony

 

[JohnD]

I know that sink traps get blocked with tealeaves, peas and bacon fat, but the waste from a dishwasher is filtered, hot, not greasy, and contains a strong detergent, so I wouldn't expect it to block, especially if it goes into a standpipe.

I was actually considering the benefits of putting the dishwasher hose onto the sink trap, to keep it clean.

 

[Kes]

Hi,

Tea, peas and bacon - now that's what I call a decent diet! Yes, I read somewhere that a dishwasher is better for septic tanks (which we have, by the way) as the high temps turn grease into soap. Magic, eh?

The old dishwasher hasn't overflowed in 18 years, so I think I'll learn to stop worrying. Oh yes, you know those silly push-in fittings, like I have on the plastic pipe feeding the tap filter, how often do they pull out and flood the cabinets? That's a joke by the way, or at least it's half a joke....

Rgds.