Helium will disappear in a balloon over a few hours. If a closed container is filled with helium will it stay active and for how long? I need to float a duck house in a pond, using atmospheric air pressure will not support it. Will a 4 inch x 10 foot pvc pipe filled with helium instead of air possibly float it? Not knowing the weight of the house and platform I can't give numbers to calculate by, so how much weight will a 4"x10ft pvc pipe closed and sealed air/water tight float? And for how long?