OK to connect basin waste pipe to bath waste?

[0-----Mikey-----0]

Hi

THE BACKGROUND
After seeing how ropey my old bathroom toilet looked beside the new pedestal basin I installed last week I decided to fit a shiny new close-coupled loo (and a new floor, tiles etc ...one thing kinda lead to another).

I knew I'd have to re-route the waste from the basin as the new toilet cistern will block the existing path to the soil stack, but the problem is that, having demolished the tiled enclosure that the previous occupants had built around the pipework, I can now see that there's no way I could access the soil stack to fit a new waste pipe where it'd need to go.

THE QUESTION:
There's a 40mm waste pipe from the bath that I could tap into, but I don't know if this is "the done thing" (I'm now't but a DIY-er so haven't a clue about building reg's). The only issue I could forsee is that the water from an emptying bath could create negative air pressure and syphon the water from the trap of the basin ...from what I've read about anti-syphon traps I reckon fitting one to the basin should prevent this, but as that's not strictly what they were made for I figured I'd seek some wisdom from this forum?

Also, if this is a fine way to go about it, could anyone tell me which (if either) is the better way to make the connection ...tapping into the 40mm pipe with a boss, or somehow fitting a tee-joint and 32mm adapter?

Thanks in advance,

Mike

 

[ChrisR]

Better not to connect them together, but sometimes you have to.
What are the pipe lengths?

 

[0-----Mikey-----0]

Hi Chris

Bath to soil is a smidge over 2metres, the basin wast would need to connect into that anywhere between 50-90cm from the soil pipe with a vertical drop from the basin trap of about 45cm.

Mike

 

[Slugbabydotcom]

Fit an anti vacuum trap on the basin. This will allow air in when the bath pulls negative pressure on the trap and reseals when the vacuum stops.
A 40mm tee and a 32mm reducer is an acceptable way of joining the pipes together. The tee should be a 'swept tee' and fitted the right way round so that it directs the water from the basin towards the soil pipe.
If you have any problem with positive pressure on the bath when you empty the basin then fit a HepV0 valve to the bath

 

[leakydave]

would one of these be of any use to you here? http://www.multikwik.co.uk/products.php?keywords=MKWCBS

just a thought...

 

[0-----Mikey-----0]

Thanks for the advice.

I went out and bought myself an anti-vac trap and all the joint and pipe I'll need then discovered that my new close-coupled loo stands 10cm away from the wall when it's connected to the waste pipe. A swan-neck pipe would save me the 10cm but I can't fit one because the hot-water pipe runs directly behind the existing toilet waste pipe with only a 2cm gap between them, so I'm either gonna have to develop some plumbing skills pretty quickly and divert the hot water supply pipe a few cm higher, or I'm gonna have to cop-out and make a tacky MDF box to bring the loo and basin that extra 10cm from the wall

...and all this because I wanted to fit new taps to my old basin!

Cheers,

Mike