I'm no vet, so you should consult a vet who's experienced with rats to address
any of your health concerns.
Red mucous : A dark reddish or brownish junk around the eyes and/or nose usually
means your rat is under stress of some kind. Keep your rat in a less stressful
environment, treat it extra-special, and give it a few days. If your rat is still producing
this mucous, give your vet a call.
Tumors: In my own experience, females are more prone to tumors; especially
beneign mammary growths. These may be surgically removed, but all surgery,
no matter how minor, poses its own risks. Talk to your vet about all of your
options, and about the risks associated with surgery.
Myco: I've not yet had a rat that died or became noticeably ill with Mycoplasm,
but it's a fairly common disease, and all rats carry the organism within them.
Again, for more detailed information, pick up the telephone and call
your friendly veterinarian.
Domestic pet rats are strictly INDOOR creatures. Never let them outside in such a manner
that they can escape, nor purposefully dispose of rats by throwing them outside.
They are not ready to face all of the predators and climactic conditions they'll
encounter, and will tend to live a VERY brief life from that point on.
Keep your pets in a comfortable location - 70F (21C) is about right for them.
Never put a cage or tank in direct sunlight - the interior will heat up like an oven and
your rat will die a horrible death. On hot days, you can put a bowl with a couple of ice
cubes in it in their cage; put ice and water in their water bottle, and even feed them
some frozen vegetables (their version of the classic summertime Popsicle).
Never, ever leave your rats inside of a closed automobile in the sun.
It can only take a few minutes, and you'll come back to your car and find
all that's left of your beloved pets is a cageful of corpses.