Last fall I replaced my drain hose with a new one that has one of those almost clear elbows where the hose connects with the ground fitting. Since then I have noticed that when I drain the black tank the elbow runs completely full until the tank is nearly empty, then it drops to about 1/8 full until it finishes. Then I close the black and open the grey and the elbow runs half full for awhile, then down to 3/8, then down to 1/4 full, etc.
I know I could open up the tank area and check the piping design, but it's a major job, so I'm hoping someone knows the answer. Is there something in the design of the gray drain piping that would cause this? I can see the black piping being large and straight, but it doesn't seem that the grey should be that restrictive.........I thought perhaps the grey valve was only opening halfway, but I have timed the electric drain valves and they make noise for the same length of time, both opening and closing.
I even went up on the roof and ran a snake down the vent pipe........ideas?
