I never took any photos of my water/sewer station on the bus - but here is the RV for you RVing buffs www.beemaster.com/bus.html
The ideal procedure for tank flushing according to my boo, and it is what I do in my rig when traveling:
Build up the level of the Black Tank to build up as much HEAD PRESSURE (for cyclonic action) as possible and also get your gray tank pretty full.
Dump the black tank as much as possible, close the black gate valve and open the gray tank gate valve - this flushes the hose with the soapy water from the gray tank. Secure the gray tank, add 2 gallons of fresh water to the toilet and about 8-12 ounces of toilet chemical treatment. This is a must: spend the money and get a good chemical treatment, it breaks up all the solids and turns the whole mess into a tolerable yet contained sanitation system.
I also have a black tank rinse system which allows me to hookup a water hose (not the same hose used to supply fresh water - they are special WHITE COLORED hoses that DON'T allow "Hose taste and smell" to get to the fresh water tank) but you hook a garden hose directly to a fitting on the outside of the black tank which has a rotating sprinkler rod inside the black tank which greatly helps breakup the stuff that gets left behind.
The most important product in this whole process though is the black-tank odor control chemical - I do not like the Environmentally Safe stuff, sorry but it does not work nearly as good or as long as formaldahyde based chemicals.
I put about 12 ounces in my toilet with about 2 gallons of water after fully cleaning the black tank and I'm set until the black tank is full again (60 gallons later).