Dishwasher Wastes

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.....

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.

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.

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.