I dunno what the black gunk was. Maybe it's from my black rubber garden hoses? Do they deteriorate from the inside? I don't leave them out in the sun or the weather, I learned that the sun eats rubber. No matter. My husband re attached the pump to the fiberglass housing the BATTERY, not the hot water heater. I found it irritating that Casita merely slapdashed it, just haphazardly screwing and a flat backed pump on a round housing...that's nuts. But I've learned my Egg is definitely a Friday afternoon trailer...we've found so MANY things that Casita just botched, or didn't give a damn how it was constructed or installed.
Anyway, we hooked the pump back up, inserted the now nice and clean filter and voil `a, it pumped like a champ and the dB was much, much lower. It was far quieter than ever, and we've been using the camper for 10 years now. How I missed it the last time I cleaned the filter (a few years ago) I don't know, except for the fact that I was underneath the mattress on my belly with a flashlight, accessing the filter. This time we wrestled the mattress out of the camper so we could have plenty of room to work on the pump.
Even more frustrating, there is nothing on the 'net regarding actually cleaning teh filter. I think Euphoria posted it years ago but I was unable to find it.
And more frustration..the pump is a Flojet 3526-144. Flojet no longer makes it. Indeed, I went to Baydo's with the filter in hand, wanting to get a backup one, and the one behind the counter had no idea what it was. But for that matter, she had no idea what an O-ring is, that was the second thing I wanted. I had to explain an O-ring to a woman at an RV sales/service facility. Ohhhhhhhhhhhhhhhhkay.
When I need to replace the pump, what do I replace it with? I guess I'll have to call Casita.