GRAY and WASTE HOLDING TANKS??

Black and gray tanks are "waste" only tanks. They hold the dirty water/waste from your shower drain, sink drains and toilet. Toilet water/waste goes into black tank and sink/shower water drains into gray tank. You don't fill these tanks from outside your trailer, they fill on their own as you use your plumbing. Your fresh water tank can be filled through your fresh water inlet outside your trailer and is used to carry fresh water on board to use your plumbing system when city water is not available. The fresh water tank uses the water pump to transport water from the fresh water tank through the trailers plumbing.

I'm a slow typist too! Glad you got your answer. Happy camping!!!