See the full article, Oil Tank Pressure, in the REF section of the Sportsterpedia.
There should not be any noticeable pressure in the oil tank.

During normal operation;
With the tank cap / dipstick removed, tank pressure is vented to atmosphere from the top of the tank.
With the tank cap / dipstick installed, tank pressure is vented to the cam chest.

During shutdown;
The oil tank vent is connected to the cam chest and the cam chest is vented out the breather valve(s) in the cam cover or heads, respectively.
So if you have pressure in your oil tank and the vent to the cam chest is not blocked then the cam chest is also pressurized.
If the cam chest is holding pressure, then your breather valve(s) can not be venting properly.

Bottom line is that if the vent system is working properly, you shouldn't have excessive pressure build up in the oil tank. ¹⁾

Oil hose sizes: ²⁾
Feed hose: 1/2 “ at tank but changes to 3/8” prior to pump.
Return hose: 3/8“ from pump to tank.
Vent hose: 1/4” from cam chest fitting to tank.

In the pics below; ³⁾

• A is the drain
• B is the feed
• C is the vent
• D is the return

94-03 Oil Tank Fittings 4)	2004-2013 Oil Tank Fittings 5)	2014 and Up Oil Tank Fittings 6)

Be careful of the feed line in the FSM diagram as it is mis-leading. ⁷⁾
Feed comes off the oil pump, under the engine, tees to the drain and up to tank.
The oil pump scavenger (return) is on the top of the oil pump at the front fitting.

On the tank;
The feed is the big nipple (1/2“) on the back side. ⁸⁾
The return is 3/8”.
The vent is 1/4“.
The return and vent lines on side of the tank facing the front of the bike.

02 oil pump fittings labeled 9)

There is a dedicated drain hose from the oil tank.
It comes out from the tank, makes a 90 degree bend to the rear and fits into a cylindrical plug welded to the underside of the battery tray.
(on the rear part of the tray, near where the batter strap is fastened) ¹⁰⁾
You should see the oil feed fitting on the bottom of the tank from the chain guard side.
The drain fitting is at the bottom of the sheet metal that forms the back of the tank.

Engine oil drain hose location on a 1989 XLH 1200 11)

There is a tee in the feed hose (near the frame on the left side of the bike) and the drain hose comes off that tee.
There is a steel plug welded to the rear of the frame under the swingarm.
The drain hose fits over that plug with a worm clamp to hold it there.

Oil return and drain hose 12)	Engine oil drain hose location on a 1998 1200S 13)

There is a plastic clamp (33123-04) from the bottom frame rail that has a hollow stud for the oil tank drain hose to clamp onto.
The drain hose is anchored up inside the lower rails.

Drain clamp on 04-05 models 14)		Wider view 15)

Note:
The problem with the design is that if the plastic clamp breaks from fatigue, the hollow stud will allow your oil to leak out onto the ground without warning while you're riding. ¹⁶⁾
It only takes a minute to pop the clamp off the frame and inspect it for any evidence of impending breakage.
You can install a steel hex head bolt in the hose instead with a hose clamp securing it and let it dangle between the frame rails like the 06 models do.
This would be considered good preventative maintenance.

In the pic below, you can see the broken hollow stub that fractured off the frame clamp.
This got changed to a solid plug for the 2006 model run, but with the same part number. Others could have the same issue.

Also, check the drain hose near the motor mount. It can lay against the rear motor mount.
Vibration/friction/heat from the mount can wear right through the hose. ¹⁷⁾
You can replace the rubber hose if needed.
Just drain the oil so that you can get the plug off the end of the hose and pull the hose up through to the spot in front of the battery.
Getting the clip off may be difficult.
After you cut/pry the clip off, remove the rubber hose from the plastic one.
Get a piece of 11/32” hose from the auto supply store (header drain hose maybe?)
Cut it to the right length and install it on the plastic hose.
You can also cut it 1“ longer to have more to work with when draining for an oil change.

Broken oil drain clamp 18)	Drain hose hole worn in by the motor mount. 19)	You can also replace the hose clamp with a fuel injection clamp. It won't chew into the hose as much. 20)

The MoCo eliminated the clamp itself and went to a solid plastic plug (33123-06). ²¹⁾
It has a small head that hose clamps into the drain hose and dangles between the bottom frame rails.
It just barely peeks below the frame rails. You can cut the hose a little shorter so it doesn't hang too far below the rails ²²⁾

The plastic plug was updated (33123-06A).

09-up oil tank drain plug 23)

This is basically a valve you put in place of the drain plug on a car/truck oil pan and attach the hose to open the valve to drain the oil. ²⁴⁾
Fram doesn't make them anymore but they can still be found on the net at times. Look for the one with 1/2” x 20 threads.
The threads on the brass coupling fit can be slid in to the existing drain hose. You can use a couple clamps to secure it into the hose.

It comes with a dust cover when not in use. The orange drain hose is the fitting that opens the drain plug.
Unscrew the dust cover.
Screw on the orange hose which opens the valve to drain the oil.
Unscrew the drain hose (closing the valve) and replace the dust cover.

You may want to cut some of the orange tube so it drops in it good location.
You'll have to figure a way to mount it once installed though.