try 6" DWV (drain,waste and vent) also called thin wall. the big box may or may not carry it but that what I.ve used and the nipples work with the 6"flex. also , if your tired of waste gates getting plugged with sawdust in the corners so they don't close all the way, try using a y , a nipple and a cap at each connection. as fast as a waste gate, cheaper and non clogging, plus you can use each connection as a cleanout if necessary.