Why not have it drain into a closed top container? I'm about to set that up. My drain valve will have a hose running to a gallon milk jug with a hole cut in the plastic cap. Then, seal around the edge of the hole to make it reasonably air tight.
I had that problem a while back so I put a box of baking soda in the corner of stand. I also occasionally run a small air ionizer in the fish room if I think it's smelly.
<p style="text-align:left">how long seance you cleaned the overflows on your tank you could be smelling it from there
maybe a spill or mildew but you probably just need a bath than