what is this?

[Rose Mary]

was planning on heading out today but now for some reason water pump
isn't working. drat...thought we were set to go. Hope I didn't burn it
up, had let the water get down so I could add fresh (don't think it was
left on but it could have been)
anyway no pumping water, tho of course when I am connected to water it
flows, just not certain we will have a water connection where we are
going.
I am hearing a hiss and when I uncovered the water tank & heater found
a round item next to the wall (about 3" long and 2 " diameter, which is
black, red & silver) the hiss seems to be coming from it. When I put my
finger underneath it I can feel the air, there is an opening about the
size of the end of finger.....
I took a digital pic but haven't managed to get it uploaded to this
site.....
help?
Rose Mary
82 FC 33
Oregon