plumbing is kind of an art - yes you do need a tee "durso" unless you want your overflow to be loud. If you are unsure about what to buy, find the plumbing guy in HD and tell him what you wanna do. Alot of the time they can come up with something that you never even thought of. I found that not all HD's carry the same plumbing stuff - same with lowes. So if you go to one HD and they dont have what you are looking for, then go to another. For more info on durso's put it in a search engine and see what comes up.