This is 4 inch end cap and the "draining" end of grow bed that goes to fish tank. I used 2 rubber washers for sealing the fitting and it does not leak. The cap does because I have no sealant on it but it is dripping into the fish tank below so I am not worried about a tiny drip.
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Picture below:
The white PVC in tank is 4" thin wall I cut down the center (end to end) it is split in 2 pieces then
and these make great little hide outs for fish. PVC is great stuff you can do many things with it. [attachment=1:3586iwv5]Picture 022.jpg[/attachment:3586iwv5]