The ultimate standard, that is the one that cleanliness levels of components are set to achieve, is ISO 4406. The level of cleanliness of the system, under 4406 is measured as the number of 4,6 and 14 micron particles per ml of fluid.
Part cleanliness, including tube and hose, is measured in quantity, type, gravimetric level and size. The standard for automotive part cleanliness is ISO 16232. Individual standards on part cleanliness are usually derived from this standard.
Projectiles are not 100 percent efficient. The only way to clean tubing is to hot flush the tubes/pipes with turbulent flow. Clean is a relative term of course and it is up to the customer to provide clear requirements of the level of cleanliness that they need.
Where super high levels of cleanliness are required, the builder of the system should specify the level of cleanliness required and they will flush the system themselves. Controlling the levels of contamination serve to reduce the time required to flush the system.
Equally, where cleanliness levels are not so high, the customer may provide lower levels of cleanliness requirements.
If you are being squeezed by your customer to provide clean tubing, you first need to have the debris on the projectiles analysed to find out what it is, then take steps to remove it.
It’s all relative and the first thing to do is to establish what level of cleanliness you are trying to get to against ISO 16232 or it’s derivative.