I've always used bleach, usually a dilute solution but sometimes I spray it on neat and scrub the gunky bits with a toothbrush before rinsing under hot water. I've never had a problem with residual fumes and it's always worked well for me. I've got an Octagon 20 and after each hatch I scrub out the base and rinse, and wipe the top half with a bleach solution dampened cloth, then a cloth sjust soaked in hot water to wipe the bleach away.
Every third or fourth hatch I dismantle the base section and the top half of it completely to clean it thoroughly. I reduce it to a scary looking pile of component parts so I can clean properly round the heating element and fan and sensors. It takes a while but I think it's worth doing...