Somebody earlier on quoted a 1 to 1.5cm diameter for the galley drains.....
Jeez... maybe for the design they should have called in the local plumber, instead of 'design' engineers.
A few remarks.
- Typical domestic sink drains are about 4cm diameter, so unless you start throwing in solid objects (such as tea bags, e.g.), coffee grounds and suchlike generally get through.
- Unless you keep hammering in the notion, of how 'fragile' the galley drains are, all the time, cabin staff will treat the galley sink as their kitchen sink, which they know can take a bit of abuse.
- What are these little "chopper" devices called that 'mulch' everything thrown down the sink? Many American sinks have them, being connected to small-bore drains. They're rare in Europe, which is why I can't remember what they're called. Why don't all galley sinks have them?
- As to the happy bacteria, products like 'DeStop' or 'Domestos' put an end to them in domestic drains. What is being used in aircraft systems?
Maybe aircraft plumbing designers consider themselves to be at the bottom of the totem pole, and just don't bother?
Or maybe the personnel dealing with those systems have the same kind of inferiority complex?
Considering how much damage has been done over the years by leaking and overflowing plumbing in aircraft, maybe it's time the mentality changed?