Hi Larry - I'm not sure how, exactly, the back-fill was performed - I was in the coach. I just know the plumber used my site's fresh water to somehow backfill. He had told us to keep an eye on the toilet level, but the flush vent was closed. I was in the kitchen so I could relay the 'stop' when my friend in the bathroom saw water coming up into the toilet. The kitchen sink and bathroom sink backed up at about exactly the same time the water rose into the toilet bowl. Suzie yelled, I yelled and the plumber almost fainted! Seems wrong to me, still, but what do I know...I just use the thing, I don't "design" them! If the designers want to have extra liquid to flush the stuff, why don't they just make the grey tank drain thru the black. Rhetorical...no answers needed!
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