i bought a whatman klari-flex bottle top filter and i used a small pump to pump some stuff through it for filtration.... it went good for the frist 100 ml or so but after that it slowed to a hault. After the next houjr or so i got another 100 ml....after looking at it, it seemed to crack. does anyone have a suggestion for a good electric pump to use with these units or any other bottle top filtration? any idea what psi is needed for optimum flow?