Bath and sink connected on same pipe – bath gurgling when sink emptied

bathroomdrain

The bath and sink are connected to the same pipe as shown on schematic below – pipe has a gradient downwards towards the main pipe (yes, I have found some people fit it with an upward gradient!).

When I empty a bucket into the sink or empty a full sink, the bath starts gurgling or burping, sending water through the waste outlet into the bath. Note there are no blockages anywhere in the system.

  1. Is there anything that can be done to prevent this without connecting all bath components directly to the main pipe?

  2. Can multiple bathroom sinks, baths, showers etc. share a common drain pipe and if so, are there any rules?

UPDATED SCHEMATIC after posting to show toilet – this works fine and does not cause any problems to the sink or bath when flushing.
updated

Best Answer

T Piece

Is the bath trap "gurgling" because of bubbles coming out of the trap, or because of air being sucked into the trap?

This is important, because I suspect the T Piece could be the issue. Since it's not a gentle bend pointing toward the waste pipe, when the water hits the T, it could go upstream, compressing the air up to the trap, and bubbling out.

Alternatively, if the force of the water is sucking the air from upstream, the trap will lose water and air will get sucked in from the bath.

See this page about vertical waste drops. It says a Sanitary Tee is incorrect for vertical downpipes:

When connecting any vertical waste drop to a horizontal run the proper way to do it is to either use a Wye & 1/8 bend (45 deg), or a Sanitary combo. A sanitary combo is a combination Wye & 1/8 bend already made in one fitting.

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