OrnaVent™ is our new vent disguise with the purpose of decorating the high or low vent on Advanced Enviro-Septic®, Enviro-Septic®, Simple Septic®, and EnviroFin™ Septic Systems. For more information on the importance of venting on Presby Septic Systems visit the Venting page. Fits Sch. 35 &40 pipe. 4″ pipe diameter.