I located pipette tips that have a wider opening on bottom  for viscous
solutions.  

Fisher has these, MBP is the company, OR you can cut the tip off a blue
pipette tip to produce the wider opening and use the 1000 ul autopipettor,
then for totally accurate volume, aspirate the Tween 20 (try to not get the
whole tip into this goo!), wipe excess from tip with Kimwipe, and dispense
with multiple up and down rinsing.  This is an old med tech trick from days
long gone. 

Unless you absolutely need that totally accurate volume you would have to
use a volumetric flask ala quantitative analysis technic. I don't think you
will be off by much without all the fuss of wiping, although rinsing is
good practice.  Making solutions up in beakers, flasks, and even Wheaton
bottles with markings on side, and graduated cylinders is not very
accurate, but adequate for most histology purposes. I have gone to the
plastic disposable Pasteur pipettes for ease, speed and see no problems.  

Enough on this stuff!
   
Gayle Callis
Veterinary Molecular Biology
Montana State University
Bozeman MT 59717-3610
406 994-4705
406 994-4303