The female side of a PVC glue fitting is tapered, so the further you insert the male pipe (cut it out Theo), the more resistance you get from the female side (I mean it, Theo). I'm sure you already know this.
When the 2 pc of the connection are just pushed together you are not likely all the way to the bottom of the female side, so less overlap. This in of itself is not a big deal for your application. What I have often seen (and experienced) is that the relative ease with which you pushed them together will not be the same ease when you REALLY need to pull them apart. Whether it's an accummulation of minerals from the water, or the 2 pc of PVC swelling at a different rate, it always seems to be a bear to pull apart when you need it.
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My thought was to glue in a 12" piece of pipe into the female elbow. Then install a rubber coupler between this new nipple and the intake pipe.
