Always, and only, hand-tighten a bulkhead. Using tools just applies too much pressure MOST of the time (because most people do not do it right, or dont know how to). A good solid hand-tightening will almost always work, as long as your bulkhead or gasket are not defective. Using tools also allows you to run the risk of cracking the bulkhead or nut (especially small cracks you cant see). I've seen this often.
People do/can use tools, but I wouldnt want to go more than 1/8th of a turn... certainly much less than 1/4. A non-defective bulkhead with a decent gasket (provided the glass on both sides of the hole, hand-tightened, should seal every time.
Plus, making the gasket 'squeeze out' is a bad idea. The gasket is not made to be crushed, the gasket is simply made to make a seal. The harder you 'smoosh' it, the more deformed it becomes, and the lower quality your seal is. Some bulkheads also have gaskets that dont quite reach the edges of the collar itself, so a rule for a 'squeeze out distance' will be innacurate.
Please, only hand-tighten, make sure all materials are in good shape, and you should be without leaks! If you simply cant reach a spot to snug it up by hand, then you can use a tool to turn it in 1/8th increments till you see no leak, but you should NEVER have to 'force' it hard at all if using a tool/pliers.
Chris
