I see a lot of 20 Lb propane tanks in the trash
these days. .... I am looking for ideas on what I
can use them for.


20 gallons is approx. 160 lbs. water displacement.

If those tanks weigh 40 lbs., that leaves 120 lbs. of net bouyancy.

If a small house weighs 12,000 lbs, then 100 of those tanks could float a
small house.

So, my suggestion: strap 100 of them under a small house, put a sail on it,
and take a trip to the South Seas.