Dishwasher Wastes

[jtaunton]

Apologies if I get my terms wrong here, but I'm not a plumber so bear with me.

My dishwasher waste is connected to the sink waste, just above the U-bend.

When it starts up, I think that it has a quick pump to clear anything out of its waste pipe and usually ends up just pushing some air out, which in turn pushes the water out of the U-bend and makes the sink smell terrible. (I'm guessing all this but it seems to make sense).

Also, when the dishwasher drains, it sometimes bubbles up through the sink.

I guess its done like that for a reason, but what are the pitfalls of connecting the dishwasher waste to the far side of the U-bend, maybe once the pipe starts its downwards run.

Or any other solutions to the problem.....

 

[felix]

There are drawbacks to connecting the waste above the U bend, not least of which is that a blocked U bend will send the dishwasher water up into the sink. This must be what's happening to you because that pumped air could only push the U bend contents downwards. Worse, if that bend is well and truly blocked - and if your dishwasher uses more than a sinkfull of water - you'll set the thing off and come back to a flooded kitchen!

It's always better to connect an extra waste below your U bend if you can but you'll need to put a trap in as well. You need an open ended vertical pipe into which you hang the end of your dishwasher waste. These things are readily available with a trap already fitted at the bottom. Waste plumbing is a doddle with push fit components. Solvent weld is messy and you only get one go. You'll need to find out what you've got.

 

[jtaunton]

OK - I'll give that a try, thanks.

My whole waste acts a bit funny, because the sink acts as if it is blocked, by bubbling when I run the tap and not draining properly, but I am also fairly convinced that it isn't. If I fill up the sink with water (whilst the plug is out) it gets to a certain level and then suddenly the waste seems to unblock and all the water runs away no problem.

Have taken the U-bend off and no blockage there, and I've even tried one of those gas-powered unblockers a couple of times. As soon as you've done it the water runs away fine, but within ten minutes or so it is back to acting blocked again.

 

[felix]

You've got an airlock somewhere in the waste pipe. This could be caused by a dip in the pipe or it could be that the open end is underwater in a blocked gully. The result is the same either way. Air is trapped in the pipe between the U bend and the dip or submerged end. Your sink must fill to a certain level before the water pressure blows this out. At this point the sink empties normally but it won't last. Do you hear a loud gurgling from the trap as the last of the water disappears? That's air being sucked back in.