waste plumbing in bathroom

[tim bunch]

I have recently installed a new bath and sink in the bathroom, as part of the renewel I wanted to resite my sink and to do this I had to connect my sink waste in 32mm into my bath waste 40mm using a reducer.
My bath waste is about 1.75 metres run from the main waste pipe outside and my sink tee's into this waste about .50 of a metre before it goes outside

When I release the a bath full of water from the bath I get a loud gurgling noise for want of a better discription from the sink plug what have I done wrong please?

 

[TicklyT]

This can happen. The flow from the bath is causing a partial vacuum at the basin waste, and drawing the water from the basin trap. Some solutions are:-

Fit an air admittance valve in the basin waste.
a 32mm valve fitted to a tee just behind the trap in the basin waste.

Fit an anti-syphon trap in place of the basin trap.
These either incorporate an air admittance valve, or are designed to hold more water, so will still seal after the trap is 'drawn'

Fit a 'dry trap' that uses a membrane seal instead of a water seal.
Something like a Hep VO trap

Fit a larger tee and waste pipe downstream, say, 50mm.
The larger bore pipe reduces the velocity of the flow, so the partial vacuum isn't enough to draw the trap

 

[tim bunch]

thank you for that information, I will look for valves etc this week