Weight needed to push a 1 m³ styrofoam cube 1 meter deep in a water column

[alibaba2]

a little brain teaser..

hi ...i'm having a hard time figuring out this one. see attachment pic. a water coluumn, square based tube ( 1 x 1 meters ) - height 10 meters. what will be the amount for the red weight at one side of the see-saw in order to push a styrofoam cube sized( 1x1x1meters=1 cubic meter) . the force must be sufficient to push the styrofoam inside the water column 1 meter up (so it will be at 9 meters depth).
theoretically there is no friction, and there is a seal blocking the water from flowing down and out of the pipe.

ideas?
thanks

 

[Troels]

the force must be sufficient to push the styrofoam inside the water column 1 meter up (so it will be at 9 meters depth).
theoretically there is no friction, and there is a seal blocking the water from flowing down and out of the pipe.

I don't get this one: If there is a frictionless seal between the styrofoam and the cylinder, then you can't push the foam "into" the water; the foam will act like a piston and you'll simply lift the entire column

 

[alibaba2]

ok, forget the frictionless seal detail, what i mena is there is no loss of water...i.e. all water leaked out below is compensated above, so water level remains constant.
thanks