Because of the nature of where they are installed both the Single and the Twin feed can be blocked up by accumulated dirt grease and grime from the rear sprocket if the sprocket is not cleaned prior to installation.
The action of wheeling the bike backwards is remarkably effective at pushing dirt from the sprocket back up inside the nozzle tip(s), however if the sprocket is clean to start with the action of the oiler feeding clean oil to the sprocket will keep this area clean and this won't be an issue.
This is the Single nozzle
Note the end with the black band around it has a small barb, this is the end that goes into the hose, the barb ensures the nozzle stays in place and makes an air tight seal with the hose.
To clean the single nozzle remove it from the hose and wash in clean warm soapy water, you can poke out any debris that's lodged inside the tube at this point, blow though the nozzle to make sure its clear.
This is the Twin Feed nozzle (discontinued)
To clean the Twin Feed nozzle carefully remove the nozzle from the hose - Do not pull the nozzle from the hose by gripping the flexible black nozzle tips or you will damage them but instead grip the hard black base of "Y" piece and gently ease the nozzle out of the hose.
Clean in warm (not hot!) soapy water and blow through to ensure the passages are clear. Dry and replace in the hose.
Do not use harsh chemical or solvents as this may damage or distort the nozzle tips, using a synthetic oil or automatic transmission fluid can also damage or distort the nozzle tips.
IMPORTANT - When installing the twin feed nozzle it must be aligned so that the sprocket is central to the nozzle i.e. both nozzle tips must touch the sprocket at the same time. If it is not properly aligned then there will be an unequal pressure on one nozzle leading to premature wear and eventually you will find that one tip will miss the sprocket entirely. See Fig 1 and Fig 2 below.
Fig 1. Nozzle centralised over sprocket. The nozzle tips are resting on both sides of the sprocket face, both tips are exerting the same pressure against the sprocket face resulting in very little wear even over long term use.
Fig 2. The nozzle was not centralised over the sprocket. Incorrectly aligned at installation, one nozzle tip has worn away and due to the unequal pressure exerted against the sprocket face the unworn nozzle (right hand side n this case) has "moved" away from the sprocket so that its not touching at all.
Fig 1. Correct Alignment
Fig 2. Incorrect Alignment