I have a manufactured home with a full basement. The basement has a bath area built in, but not complete. The ceiling is not yet installed. I can see the main drain pipe which runs horizontially along the interior of the out side wall. Another main drain pipe runs down from this to the floor of the basement and is connected horizontially along the floor of the basement along the exterior wall. The drainage to the septic tank is still below the main drain pipe in the basement, which runs to the septic system. My question is can I just connect the faucet, toilet and tub to the main pipe in the basement without venting. Would the venting upstairs work for the basement? If not how would I go about venting the basement?

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Originally Posted by Quinnexiter

I have a manufactured home with a full basement. The basement has a bath area built in, but not complete. The ceiling is not yet installed. I can see the main drain pipe which runs horizontially along the interior of the out side wall. Another main drain pipe runs down from this to the floor of the basement and is connected horizontially along the floor of the basement along the exterior wall. The drainage to the septic tank is still below the main drain pipe in the basement, which runs to the septic system. My question is can I just connect the faucet, toilet and tub to the main pipe in the basement without venting. Would the venting upstairs work for the basement? If not how would I go about venting the basement?

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The drainage should already be in place for the toilet, tub/shower and lavatory. However, I don't understand, "I can see the main drain pipe which runs horizontially along the interior of the out side wall. Another main drain pipe runs down from this to the floor of the basement and is connected horizontially along the floor of the basement along the exterior wall."
Are you telling me the house sewer's above the floor line?
You may not tie the basement vent into any of the pipes coming down from upstairs. They are drainage stacks and not vent stacks. If you were roughed in properly then you will vent the group off the lavatory tee. This vent must run out the roof or revent back into a dry vent.
However there's a bright spot, if local codes permit you may install a AAV (air admitence valve, (see image) in place of the vent pipe. This AAV would mount on the lavatory tee.

Good luck, Tom