Easiest way, but probably frowned on, is to open the previously mentioned galley tank valve, remove the cap from the sewer connection on your rig, start the washer on the rinse cycle, and if water comes out the sewer connection, you are good to go. You will have to be ready to stop the washer (see instruction manual or flip the breaker in the breaker panel) when the water appears. I guess to be "politically correct" you could put a bucket beneath the sewer outlet to catch the water!
Bingo
__________________
Bingo and Cathy - Our adventures begin in the hills of WV. We are
blessed by our 2014 3850FL Big Sky (previous 2011 3750FL and 2007 3400RL) that we pull with a 2007 Chevy Silverado Classic DRW CC dually.