My post seems to have vanished so I''ll try again.

My kitchen sink connects into the foul drain via a gulley (if that's
the right word - it's an open square hole with brick surround at
ground level with a U bend below ground). I want to change this
gulley connection to one that is sealed. (There will be a
conservatory over this area).

To do this properly will I need to have a new stack (venting up high)
connected to the foul drain and then connect the sink into the stack?
I presume I cannot just make a sealed connection into the drain
becuase the sink trap might "bubble" up sewer gas.

Many thanks for your help,

Robert
amateur