I made this "bottom drain" out of some 1 1/2 PVC pipe and a shower drain. I don't really think it works like a true bottom
drain should because the dome really isn't big enough, it's in a preform which does NOT have a sloped bottom, and the flow
in this little system is not huge. But it does draw OK and only time will tell how it really works. I just put it in and haven't
put the fish back in the preform after their winter vacation inside.

Here is the assembled drain removed from the pond, you'll see later where it attaches inside the pond.
I haven't glued these peices together yet as I know I will change them..lol..The fittings are pretty tight
and I don't think they 'leak' much if at all.

Here is the dis-assembled bottom drain showing the components:
1 - 45 deg elbow with a male and female end
1 - 45 deg elbow with 2 female ends
1 peice of 1 1/2 PVC cut to the right length for the dome to sit about a half an inch off the bottom

There is a square flange around the outside of the shower drain and a collar on the inside. These will inhibit the function
of the draw so I will remove them.

I used a high rpm rotary tool called a Foredom flex-shaft with a cut off wheel and a drum sander to remove the collar inside.
I used a jigsaw with a narrow medium toothed blade to remove the flange.





Here is the stub on the preform where the bottom drain assembly attaches. I used a uniseal bulkhead fitting thru the side
of the preform. These fittings work VERY well and are inexpensive.

Here is the modified bottom drain assembly back in place! Too bad I couldn't find black fittings :-(