Siphonage problems in fitting of bath and sink All aspects of plumbing questions and answers, help, tips and information

[yrrab]

I am about to install a new bath and sink in new positions in my bathroom. The sink waste will run through a box and meet at a T junction with the bath waste. The pipe will then run off to a waste stack. I didn't think about siphonage until I read the forums on here. Am I likely to get siphon problems? Do I need to fit some kind of anti-siphon device? If so, what are they and where do I fit them?
Also, I am assuming I fit 40mm waste from the bath and 32mm waste from the sink. Is this correct?

[plumbbob]

Unless the pipe runs is very long, you are unlikely to have a problem with water being syphoned from the traps.

Far more likely you could see water rising up from the waste into the bath when the basin plug is pulled.

It is never a good idea to combine wastes, and is actually against regulations although I bet every plumber has done it at some point or other.