Carbon Steel Hydraulic Bulkhead

To set the fitting, it must be inserted through the newly cut hole from the inside of the tank so the gasket and fitting body (the flat, solid end) are on the inside. The carbon steel hydraulic bulkhead must be placed into the hole so the locknut and thread side is available on the tank exterior so plumbing connections can be made.
Sometimes tank access can make it difficult to insert fittings from the tank interior. Often, this is due to a small manway size and/or an installation location that's out of arm's reach from the tank opening.
In these cases, use a weighted string, feed it through the tank manway or lid and thread it through the newly cut hole, then guide the fitting along the string and into position.
This part of the process may be easier if done with another person who can perhaps grab the weighted string using a pole, hook, or other means and help thread it through the newly cut hole. The same procedure is recommended for bolted carbon steel hydraulic bulkheads. Note that this is the most difficult part of the fitting installation process.

With the fitting in place and threaded side out, use the locknut that comes with the fitting and tighten it to set the bulkhead. It is the locknut that keeps the bulkhead in place. Locknuts install on the outside of the water tank. Install a locknut by placing it on the threads and turn-tighten by hand.
When tightening, do not use any tools as it's important not to overtighten the fitting. Doing so can damage the gasket, fitting, or even the tank wall. When a locknut starts to feel secure and resist further movement, perform another quarter turn to one-half turn. This should be all that's needed to secure the fitting without leaking.
Thread tape is not recommended for locknuts during fitting installation. Thread tape is recommended however when connecting valves or plumbing to the carbon steel hydraulic bulkhead after installed.
On bolted style fittings, align the fitting body with the bolt pilot holes, add the face plate, then add and hand-tighten the bolts to secure the fitting in place. Now, the four lock bolts need to be completely tightened to secure the tank fitting seal. It's best if they are tightened in a crisscross pattern. Make sure not to overtighten as it can place strain and bulge the gasket which can lead to a leak.

The final step in fitting installation is to check the seal. Perform a water test prior to making any extended plumbing connections to guarantee your new bulkhead does not leak. To do so, fill the tank up to fitting level and check for water coming from around the seal. If a leak develops, loosen the locknut just enough to rotate the entire bulkhead in a clockwise turn then retighten the locknut. If a leak develops on a bolted bulkhead, check the tightness of the bolts.