Holding Tank Odor
I've thought of the dual vent concept also but my thinking is that it would only really be efficient while moving. When not moving I'm not confident it would work very well and if the pressures reverse due to prevailing breezes I could get an odor out of what was intended as the input which could be objectionable. You mentioned "garden" pumps. Are there garden pond air pumps available at retail? Where would I look for them. I checked at the big box stores and didn't find anything.