DW wife said the kitchen sink was not draining on our Imagine 2670MK. That meant it was time to drain the black tank, then the gray's. Went outside, pulled the black tank t-valve, and nothing. lifted the rhino hose at the TT outlet connection and it was empty. Closed/pushed in the black tank valve, then opened the front/kitchen gray tank and it drained and I left it open. Re-tried the black tank and got a trickle of a flow..... Now what?? Suggestions???

Thanks!
Steve