Grey tank to black tank crossover

My two tanks are on the same level and close together with a common drain. I use a cap with a hose bib on it so after I open both valves and equalize the tank levels...several times if necessary I'm able to drain the half gallon of stuff left between the valves before removing the cap. I have a hose valve on the hose bib and I put the drain hose up to it, open the valve, drain the half gallon and then remove the cap and put the hose on to finish dumping.



PS:: for those that take forever to dump with all the steps they take, in 50 years of doing this I do not use gloves. Yes, taking 10 minutes to dump is one of my pet peeves.