How to remove and replace the block.

Use a piece of wooden dowel whose diameter is slightly smaller than that of the instrument's bore. Check that its end is smooth so as not to mark the end of the block. Only do this when the recorder is dry, otherwise the block will be difficult to remove, having swollen with moisture, resulting in possible damage. If you do find the block impossible to move, don't continue but give the instrument to a competent repairer.

Put the dowel into the lower end of the bore and tap the block backwards. By putting a finger on the block you should feel it moving. Use the other hand to stop it from flying out violently and being damaged. You can also put a sock around the end of the head to catch it if necessary.

To replace the block insert it carefully into the instrument ensuring that it is exactly in line with the windway and in the right place. If it came out easily, it will go in again easily. Just push it in with your thumb, taking care not to break the end. If it resists you will have to shave a little wood off the sides of the circular part. You can do this by scraping with a sharp knife held almost vertically against the surface. The places to work on are visible, since the wood has been compressed by the bore and appears slightly shiny. Take care not to damage the top of the block, which fits in the windway.

How to hold the block

Avoid touching the top of the block, to keep it clean. Always hold it by both ends or by its sides as shown.

Cleaning the windway

For this you can use a cotton bud soaked with alcohol and a clean soft toothbrush. You can safely remove any accumulated dirt by rubbing the wood, using the toothbrush in the corners. Don't use any metal tools, which could leave marks and cause irreparable damage. Don't touch the chamfers either. This could modify the sound and speech of the recorder.

Treating fungus

This is a serious problem, which must be treated without delay. It can have a disastrous effect on the sound and cause damage to the wood in the long run. It is sometimes be caused by drying in bad conditions but can have other origins. Some woods, like maple or box, are more prone to it than others, like pear and certain tropical hardwoods. The block is often more resistant than the instrument itself.

To cure this you can use a 10% solution of undecylinic acid (which can sometimes by found in pharmacies under the name of Mycodecyl 10%).
First remove the block. Then soak a cotton bud with this preparation and rub the black spots in the windway, as shown in the picture above, until all the roughness has gone. A clean toothbrush can be useful for getting into the corners. Never use any metal tool for this job.

The windway must be checked regularly afterwards to be sure that the fungus does not reappear. If it does, just repeat the treatment. It will finally go for good.

It is almost impossible to eliminate fungus in the windway without taking the block out of the instrument because some rubbing is necessary to remove it completely and restore a smooth surface.

To help prevent fungus from forming in the windway, be sure to let the instrument dry out every time after playing before putting it in a closed case, and to store it away from any dampness .