Question: How tight should my latex seals be?
Answer: All seals must be snap tight to keep out the water, however not so tight that they cut off circulation to your feet, hands or head. If your neck seal is choking you its too tight!
To make a seal larger simply trim the latex down with a pair of sharp scissors. (See the drysuit manual before attempting this!) Before trimming a seal, you can also stretch it over a larger diameter circular object, such as an ice cream tub, and leave it for 24 hrs. This can make the seal slightly larger.
From here:
http://www.oceanrodeo.com/drysuitsfaq.html
NEW SEALS:
New neck or wrist seals may feel tight or restrictive at first but will relax a little with use. WARNING! Never use a seal that is so tight that blood flow is restricted to the head or hands. Too tight of a neck seal can lead to a life-threatening situation once in the water.
You can pre-stretch your seals by pulling the wrist seals over a small bottle and pulling the neck seal over a scuba tank or large soda bottle. 23 inches in circumference works well. Leave the seals in a stretched position for only 6 hours at a time. Tests fit the seals after the first 6 hours and repeat the 6-hour sessions as needed until the seals are comfortable. Make sure that you have applied silicone (or Seal Saver) to the latex prior to stretching. Consult your dealer if you have any questions.
NOTE: O.S. Systems manufactures 3 sizes of wrist seals and 4 sizes of neck seals, make sure that you have the correct size seal installed on your drysuit BEFORE you start any stretching of the seals.
From here:
http://www.my-town.com/learn2dive/equip_drysuits.asp
A thread from scubaboard:
http://74.52.40.173/showthread.php?t=842
Last but not least the best one with pictures:
http://www.andysdrysuit.com/howto/LatexSealCareAndUse.PDF
Now are these correct or is it all misinformation? I am sure if someone searched they could find all kinds of info saying trim only and in my research here, I do stand corrected on "most manufacturers" as it seems most actually say to trim. In my own experience with drysuits and my friends we have found that they do loosen up over time or by placing an object into the seals themselves. Maybe a call to the manufacturer is in order.
Here is D.U.I.'s write up on trimming seals:
http://www.dui-online.com/how_to_trim.htm