When draining oil from the oil tank, there is a certain amount that will stay in the engine and mix with the new oil after an oil regular oil change.
This is normally how it is done per the FSM.

However, this most likely won't remove all of the oil from the sump.
This will not drain oil from the feed lines to the engine.
The Evo case drain will not drain the sump as the drain hole doesn't enter it.

Therefore, there will be a certain amount of used / old oil that will stay in the system and will mix with the new clean oil.
This will also dilute the new oil to an extent.

The Evo case drain doesn't actually enter the sump 1)

Some would prefer that all of the used oil be removed during an oil change.
Below are some ideas on how to accomplish this.

The easiest way would be to disconnect the return oil line from the tank to and spin the engine / oil pump and let the remaining used oil collect into a container.

1. Drain the old oil from the tank using the drain hose as usual. ²⁾
2. Install the plug on the end of the hose and add two quarts of your favorite oil to the tank.
3. Remove the return line from the oil tank (be careful not to break the connectors on plastic oil tanks).
4. Remove the spark plug wires and close the gas petcock.
5. Secure the return line so the oil goes in a waste container (be sure you can see the oil pouring out of it).
6. Crank the bike with the starter until you see clean new oil coming out of the hose end (average of about a quart).
7. Change your oil filter and turn the motor over a couple revs and reinstall the return line to the oil tank using a new clamp (spring or worm clamp as you prefer).
8. Reinstall the plugs wires, open the gas petcock and start the bike for about 20 seconds to get oil circulating.
9. Fill the oil tank to bottom line of the dip stick and go for a little ride to fully warm the engine.
10. Then check the oil dip stick to see if the oil is between the two oil marks.
11. The oil line should be between the two marks on the stick. Add oil if necessary.

This works the same as above with the exception of installing an inline tee in the return hose to the tank.
Simply pinch off the hose on the tank side of the tee to allow the scavenged oil to empty into a container through the tee'd off hose.

Pre-86 scavenge oil change diagram 3)	86-90 scavenge oil change diagram 4)	91 and up scavenge oil change diagram 5)

The Rogue Chopper site sells an oil scavenger system for 2004 - 2009 Sportsters (except the XR1200).
It's not clear why it is not retro to 86 models but the filter adapter has the same threads from 86 and up.
Cost is currently $69.95 plus shipping.
All the puck does is provide a straight through route to flow the oil without filtering. ⁶⁾
If you could somehow gut a filter it would do the same thing.
The puck is nice though, made from billet aluminum but all in all it's only a tool.

It wasn't necessary to take off the rear exhaust like their video instructions tell you to do.
There is plenty of room to cut out a 1/2“ piece from the oil return line.
You don't have to feed the “scavenge” drain hose to the left side of the bike in back of the primary.
It can be snaked down the middle, next to the regular drain oil drain hose and routed it to the right side of the frame to the bottom frame tube.
An extra OEM plastic drain plug can be used to clamp the scavenge drain hose to the frame just like the oil OEM drain hose, but on the right side.

Squeeze clamps come with it but you can use worm gear type clamps instead if you choose.
After installation of the “T” fitting and scavenge hose you can drain the oil as usual from the tank drain.
Then remove the oil filter and install the scavenger “puck” in place of the filter.
Clamp the return oil line right behind the “T” fitting installed for the scavenger drain hose with the forceps provided in the kit and fill the tank with oil.
Start the bike and run off oil until it shows clean oil out the scavenge hose end.
Then you can plug the hose and attach it the frame for future oil changes.

Remove the puck and install the new oil filter as usual.

Note: The scavenge side of the oil pump doesn't seem to push a constant flow at idle.
It has a higher pumping capacity than the pressure (feed) side and the scavenge side will push out the sump contents in dribs and drabs.
(as if it was waiting for the oil to accumulate and then pump it)
Give it more throttle and flow was more constant.
It doesn't take too long to pump out a quart so the oil in our bikes circulates pretty quickly, especially at higher rpms.

Rogue Chopper Sportster Scavenger Kit 7)

Fitting at tank swapped out. 8)		Tee fitting comes with the kit. 9)