Dishwasher waste to a 32mm pipe?

[Rodolphe]

A client wants his dishwasher waste pipe connected to his washbasin, which exits in 32mm.

Knowing that it's supposed to go into 40mm, I wonder if I can do that? I mean practically, sure, but is it a very bad idea, or is it OK?

What do you guys think?

[Phil]

In an ideal world 40mm but sometimes you have make the best of what you have to work with, just make sure its not a long flat tourturous length and the wash basin drains nicley.

[Hybrid]

It'll probably pull the trap seal out on the basin.

[Destroyer2813]

My mum and dads w/m pipe discharges into the basin waste and has done for years do problems. ps i didnt do it by the way

[Rodolphe]

Thanks all for those lightning fast replies!

It'll probably pull the trap seal out on the basin.

Good point Hybrid, I'll make sure to fit an anti-vacuum system.

[chris watkins]

It will pull the trap!! but only after it has pumped the discharge from the machine back up into the basin (probably, depending where the connection id made). It not only should be 40mm but it should also be on it's own run to the stack, it may not be a problem when it is installed but any build up on the inside walls of the waste will cause problems later. Don't do it tell them it needs to be installed correctly (In line with Part H of the building Reg's).

[Paulus]

with Chris. If they still insist on going into 32mm I would still do the job as they want but make sure they understand the possible consequences. I would put it in writing so they can't deny your advice in the future if problems occur. If you don't do the job, somebody else will and you could lose a future customer.

[dsteves619]

Its bad practice but you will probably get away with it.
I personally don`t think it will blow the seal out the trap, but that does depend on how its been ran.
You could always use a hep vo check valve if you was concerned, I`m sure they are available in 32mm.

[chris watkins]

Its bad practice but you will probably get away with it.
I personally don`t think it will blow the seal out the trap, but that does depend on how its been ran.
You could always use a hep vo check valve if you was concerned, I`m sure they are available in 32mm.

They are & you could, use one. A water filled trap would more likely self-siphon rather than blow out but either way Hep vO trap on the basin waste fitting would do the trick, good call dsteves619.
If you are going to do it, just take care that the washing machine outlet hose is not air as it connects to the 32mm waste.