duel 3" sewer connections using a Sewer Solution?

I have the same set up. 1" PVC fittings fit the Sewer Solution so I made a "Y" connector from PVC with a standard water hose fitting connected to the dump end fitting, put the sewer solution on the black/grey dump, installed a 3" cap with a hose fitting on the other gray tank dump and run a standard water hose from it to the "Y". When I start to dump the black I disconnect the hose at the "Y" and cap the "Y" to eliminate the chance of black water entering the gray hose/tank.
Works like a champ.