Oil is spewing out through the Oil Fill Port Cap, and through the Port itself when the Cap is removed

Oil is spewing out through the Oil Fill Port Cap (through small pin-hole air escape devise in cap), and through the Port itself when the Cap is removed.

This is a Central Pneumatic, 2 HP-8 Gallon Model 40400. It is not used often, I've never changed the oil but have added oil as needed per the oil level indicator. I'm usually very good about draining the tank after use, but apparently last time I didn't, as there was air in the tank when I went to use it.. The oil that is spewing out of the Fill Port is Milky, and I've learned from your site that this indicates water in the oil. If I drain the oil will that be sufficient, or will further cleaning be necessary and if so, how do I do that ?
Thank you so very much for your help and this site.
Regards,
Tom
Pleasanton CA
Dry with No Humidity

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Bill says...

Tom, if oil is spewing out the oil fill tube, then my first thought is that it's way over filled.

Second, you've got air bypassing the piston seal and ingressing into your oil sump.

Drain the oil, fill to just at the normal fill line, remembering that it sometimes takes a few minutes for the oil level to indicate the actual level after you've stopped filling.

What happens then?

Cheers,

Bill