A new, properly made molecular trap or "trap pak", when added to a bottle of solvent, should NOT immediately sink. They should float...

If this happens, the trap is made from the wrong type of membrane, poorly sealed, or already wet.  They are called "sinkers" and should be immediately pulled from the solvent bottle.  However, I have only seen this occur 2 or 3 times in my 27 years of using a standard "trap pak".  

The trap needs time to "equilibrate" with the pressure difference between the solvent and the inside of the trap.  The trap will eventually sink, but only after reaching equilibrium with the solvent.

The MSSP is no different.  They float, and sometimes longer than the standard trap.  This is because the MSSP is made from a proprietary membrane material, designed as a first stage sieve.  The pores in the MSSP allow water in but NOT out, then the molecular sieves ensure the water is removed from the solvent and permanently contained.

Finally, you can speed the equilibration process up by applying pressure to the solvent bottle, or attaching the solvent bottle to your pressurized synthesizer.  Then they sink.