I use the one in this tag it's the RV Sani-Con Systems MODEL 5800-6004-HB, SKU 70224
(Same as 5800, except with twist-on fitting)
http://www.rvsani-con.com/order_online.htm
the only problem with these type tank emptying systems is it takes about 4 times longer to dump, compared to using the 3 inch hose.