Waste pipe size for a (big) bathroom sink?

[r1bena]

Hi all,

I am about to fit a new pedestal sink in the bathroom (upstairs) and I want a straight through trap, so the waste pipe runs straight down the pedestal. (I think) I would like an anti-vac one, but I've only seen these in the smaller 1 1/4" (32mm) waste size, not 1 1/2" (40mm).

What is the best size for the waste pipe of a large bathroom sink? Is 32mm ok, or is 40mm better?

Thanks in advance...
R1.

 

[AdamW]

All the ones I have seen for bathroom basin use are 32mm. I tried to fit a 40mm anti-vac trap on a pedestal sink but it wouldn't sit within the hollow of the pedestal.

I can't think of a situation where you need your bathroom sink to empty so quickly as to require 40mm traps, so you are unlikely to run into problems. I was thinking a His and Hers pair of basins, but that should have separate traps anyway.

I can appreciate where you are coming from, you no doubt like to ensure things are over-engineered/have massive contingencies. If you are doing this to ensure your wastepipe will be wide enough for any future upgrades, you can use 40mm pipe with an adaptor down to 32 for the trap.

 

[ChrisR]

Hepworth do a linear thing with a rubber tube inside - like a condom withthe end cut off. They may do an adaptor for 32mm/ 1 1/4 inch waste. If you find one let me know because I want to do the same!