Owner of a trailer that came with electric valves. Gray tank electric valve failed to open in 2008. (4 years old) Black tank valve failed to open 2010. (six years old) The gray tank for the kitchen after ten years (knock on wood) is still working.
Have to remove about 30 screws from underbelly. Crawl under and with a slotted screwdriver very carefully turn to open the valve. The slotted head is pot metal junk. I left both open. Put a hand pull valve on for the black tank. The grey tank have a valve at the end of the line. This tank is for the shower, bathroom sink and washing machine, so not a big deal to leave open all the time.