All of the fittings come through the lid, and the lid screws down to the jar. I use rubber tape around the hole for the cord, but as long as it stays upright, it isn't a problem. I am more interested in keeping the dust out than in keeping the water in.
I don't have a perfectly air-tight seal around the fittings. If I did not have tape around the cord hole, it would be open enough for dust from the intake to blow into the coolant. Not pretty when it happens. Evaporation I can deal with when needed, but with two 90cfm 120s blowing right next to the res, I have got to keep the dust to a minimum.
I have two sets of scotch-brite filters separated by another cloth filter keeping dust to a minimum in my intake. I'll have to find the picture.