Check the Hepvo valve connection. Mine had a piece of pvc pipe under the 90 degree connector that ran from the main drain line to the shower drain. Over time, stepping on the drain on one end and the pipe supported solidly (no give at all) on the other, it created a gap at the connector.
I have a few other plumbing issues if you'd like to hear them just pm me.
I have been living for over one year full-time in ours and she's holding up pretty good.
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