"Lee Brouillet" wrote in message
...
No, the bowl is the "dome" over the open drain. The air diffuser is
mounted
to the top (or bottom, depending on how you look at it!) of the dome.

Remember, I didn't purchase a commercial bottom drain: I made it from a
toilet flange. Therefore, it's just a big open hole in the ground that
needs
to be covered to prevent the vortex action. That's where the 16"
terracotta
bowl comes in. If you already have the bottom drains, and merely want to
convert them, go to Mike Singleton's site and go through his DIY section;
there's an article there about making a conversion to a Tetra bottom
drain:
http://www.livingjewels.com

I plan on building a DIY bottom drain...my original question was about a
bottom drain that included a diffuser. I have no idea what a diffuser is.

BV.