Hold, on I gotta go get some more shotgun shells....
Picture #1 - the fuel filters are down there, two of them, as noted by earlier posters.
The oil filter is on the other side, and may not be a spin-on, might be the replaceable cartridge type. If it has a bolt centred in the bottom, it is the cartridge type. Cheaper to buy, messier to deal with...
Picture #2 - this is the infamous shutter and damper control. If it controls anything else, somebody has been fooling around with your coach. Bottom valve is the release and drain, side one is the supply. Close the supply, open the release.
Yes, change that red lense to a clear one, if it works with the light switch on the rear control panel.
Picture #3 - this air connection opportunity serves two purposes. First is that it allows you to drain the first place in your air system that water collects, often ignored or , as in your case, defeated by someone's modification attempts, Those who don't use it, don't worry, the moisture will show up downstream...
Second, it is a great place to fill the bus air system by way of a remote compressor.
Note, this air connection does not always have air pressure present, unless your system has been modified. There should be one way valving at the dryer or at the wet tank to protect the air system in the event of a compressor or compressor line failure emptying the system backwards.
Notably, if the air dryer has purged, this line will be at atmosphere. Jack's advise as to teeing this off, drain on bottom and a choice of male and female connections is EXCELLENT. (Thanx Jack! Why have I been fooling with that double ended cheater for so long...?)
Picture #4 - follow the pipe on the bottom, this drains into the power steering reservoir, seen in the back with the sight glass. As posted, figure out what's already in there.
The ether cup is mounted higher, in the top of that metal elbow of the air intake. Might be there, too much shadow to tell for sure.
Pays yer money, takes yer chances!