These are 4" aerated bottom drains I 'll be making.
The first one has a 9" Matala diffuser which I like. There is not as much back pressure on the air pump with these. The cost is $90 + shipping.
A 12" AIR DISC is also availabal for $10 more.
The second one is the same except with a 9" DreamPond diffuser.
The cost $75 + shipping.
They both have 1" PVC air inlets.