spoon059 wrote:
And if the OP is concerned about pests flying up into the grey tank, he could leave it closed and just open it once or twice a season.
Don't make this mistake. A dehumidifier can generate gallons of water per day...wait a month or two, and it will have overflowed potentially rotting out the floor.
As someone else mentioned, opening a roof vent is you best bet, just get a cover, so it can be left open in the rain.
If you insist on using a dehumidifier, just get a cap with a hose connection and put a small sag in the hose. This will create a P-trap, so no bugs going into the tank...not that I would really care if they did as there is no route to the interior from the gray tank.