I plumbed my new house myself--pressure plumbing, not drains. There is more science and code to drains than I cared to learn. I would suggest at the minimum consult with a local plumber you trust. Proper venting is a must for drains to work well. There is code for plumbing and it is designed so it works properly. Not so simple. And it is a crappy job to fix it later (pun intended.)