I'm in the process of refitting a downstairs bathroom and undoing all the bodges done by the animal that fitted it in the first place 
The bathroom is an addition but is attached to the main house. The house is of 1920's construction and already has a cast iron foul stack with a vent that sticks up above roof level.
The downstairs addition has a foul drain that joins the main foul drain approx 3 metres from the vertical cast iron stack.
There is a foul drain in the floor of the downstairs bathroom that takes the waste from the toilet. I would expect the waste from the toilet to go sraight out from the back of the toilet and down into the drain in the floor. But the foul drain is in the wrong place. The was from the toilet therefore has to go out of the back of the toilet, through 90 degrees, nearly horizontal for about 3 feet and then feeds a small waste stack that protrudes from the foul drain. The small waste stack (about 300mm high) has a solvent weld air admitance valve on top of it. The whole lot is a real lash up and looks awful.
I want to move the toilet closer to the foul drain and then take the waste from the toilet straight into the drain.
After all this narative, my question is whether i actually need the air admitance valve. The valve is only approx 300mm from the floor, and is quite bulky. No other drain feeds into this section of the foul drain. There is also the vent at the top of the main stack, approx 3m away horizintally.
The bathroom is an addition but is attached to the main house. The house is of 1920's construction and already has a cast iron foul stack with a vent that sticks up above roof level.
The downstairs addition has a foul drain that joins the main foul drain approx 3 metres from the vertical cast iron stack.
There is a foul drain in the floor of the downstairs bathroom that takes the waste from the toilet. I would expect the waste from the toilet to go sraight out from the back of the toilet and down into the drain in the floor. But the foul drain is in the wrong place. The was from the toilet therefore has to go out of the back of the toilet, through 90 degrees, nearly horizontal for about 3 feet and then feeds a small waste stack that protrudes from the foul drain. The small waste stack (about 300mm high) has a solvent weld air admitance valve on top of it. The whole lot is a real lash up and looks awful.
I want to move the toilet closer to the foul drain and then take the waste from the toilet straight into the drain.
After all this narative, my question is whether i actually need the air admitance valve. The valve is only approx 300mm from the floor, and is quite bulky. No other drain feeds into this section of the foul drain. There is also the vent at the top of the main stack, approx 3m away horizintally.
