also in this model is the 2nd bathroom plumbed grey and black water plummed together?
I really dislike saying "I don't have your trailer but this is what I think"
But, from all the Cyclones I have looked at (and staying once or twice at a Holiday Inn) I am going to guess you 415 has four tanks and two separate drain discharges (3" sewer hookups).
Is that correct?
Grey #1 = bath, shower and sink. And washer dryer if you have that option in the closet.
Grey #2 = kitchen sink
Black #1 = main toilet
These three tanks should be connected to the front sewer discharge pipe.
Black #2 = half bath toilet and sink and washer dryer if you have that option in the garage.
This tank would be connected to the discharge behind the axles.
It would be a grey tank if only the sink and washer were hooked up. Connect a toilet and it becomes a black tank, but can still take wash water.
Gauges, as mentioned are notoriously inaccurate.
BTW, your 100 gallons of water tanks are two tanks connected with a crossover pipe.
As to your tank drain. I would first verify which drain is which. The only way you can tell for sure if it is draining slow is to fill and watch it drain. You can do that "watching" with a "flush king" valve.
Looks like this:
http://www.amazon.com/Camco-39062-F...&qid=1360812863&sr=8-1&keywords=flush+king+rv
These valves also serve as a secondary valve in case a main tank fails to close.
There have been issues in the past where the "plug", the piece left over from cutting the hole in the tanks for the pipes, falls into the tank and causes drainage issues.
That is best left to the dealer unless you are feeling adventurous.