Help, please: Compressor top drain

I have two pancake compressors. A jun-air, and the Italian copy of it, the Panther.
Both of which have a top drain.
So my question is in two parts. The first part is for curiosity sake.. why drain from the top, and how does it work? It doesn't make sense why it wouldn't just drain out the bottom like other compressors that I've used over the years... but the fact is , it works...
except when it doesn't.
Which is my second question (a person keeping count might argue this is my third question):
I moved my panther today, and it was heavy, and I could hear and feel a massive amount of liquid sloshing around in it. I put air in it and opened the top valve, but not much came out. I ran the compressor w the valve open. .... finally I pulled the drain assembly right off and just dumped out the compressor. Filled up a whole windshield washer fluid container, with more left to go.
So the question, why mightn't the drain be draining?
Anybody encountered something like this before. I do bleed off the top drain almost every day I use the compressor, but I suspect there may have been fluid in there when I first bought it. I can recall a sloshy feeling when I moved it.
Thank you

The Jun-air has a tube that goes to the bottom of the tank It just allows easier draining which depending on the humidity in your area should be done quite regularly like once a week. Don't know about the copy but I assume the same but perhaps it is plugged.
Also you should consider changing the oil. The oil becomes waterlogged and will leak past the seals and cause contamination in your equipment.

thanks rex..
i thought it would be something like that... but i got the panther valve off, and there was no tube going down to the bottom.. i couldnt get the jun air off. i probably could force it.. but its working fine.. so i asked.. i guess that is the problem.
thank you.

Kind of defeats the purpose of having the drain on top huh? Any evidence that the hose may have fallen off? I think it should have been a metal tube however.

My Jun-Aire 50 has a plastic hose that comes out from the collection jar on the bottom of the pressure adjustment (which feeds into a plastic bottle that came with it-oil collection) and another drain on the top of the main tank (pancake) to drain the tank with. You should drain the one on the pancake once a week. Switch off the compressor and crack the one on the pancake tee valve slowly-water/oil will come spraying out (should have an elbow aiming down) drain the tank. To make mine where I did not need to take it outside to open the valve almost all the way so it fully drains I added a length of 1/8 hose to the elbow and cut a hole in a coke bottle lid for the hose to reach almost to the bottom. I say cut because you want it to be a little sloppy so the air can get out after it carries the water out. I always run mine with the tank tee valve open for a min. to try and blow dry the tank. Close the tee valve and power on again until charged.

To drain the oil-the site glass is the drain plug, crack with wrench, tilt back a little and remove site glass. it will drain completely if you tilt it to you. To make it a cleaner, easier job get a nipple that has the same tread as the plug and extend it out an inch or two. I added small hose fitting to mine so I can collect the oil easier. Put the site glass back in and fill to half up the window.
Fred

Thanks guys.
Fred, i don't really have any problem with my Jun air.. at least not the problem in question. i do seem to be leaking a bit of oil.. it's pretty dry, after sitting for most of a year.. i may wind of sending it for servicing.. better than wasting another bottle of that expensive jun air oil (i did an oil change, just before i left for a year (sort of)