Kaiser wrote:

I undid the lower drain tap and the tank must have been completely
full of water! ;-(


Most manufacturers recommend draining the tank every day to help
prevent
corrosion inside of the tank.

The inside of the tank (receiver) can corrode and can be weakened to
the point where it is unsafe. If it should fail under pressure, it will
burst in an explosive manner, scattering metal fragments at lethal
velocities.

If the compressor is second-hand, it is important to pressure test the
receiver, with water, to a pressure in excess of it's working pressure
to ensure that it won't fail.

If it's used for work, I think the Pressure System Regulations apply. I
don't know if there's any legal requirement to inspect & test DIY
compressors, like an MOT test. It could still kill.

Anyone know of any relevant legislation?