Question for Big Foot TC userer

Actually I emailed BF and have corresponded with Grant there who says that my 1996 model is basically too old (in other words) to know absolutely about it. Many things, like the clearance lights, are no longer available, even, and the factory has no new source for them, so my unit's bit of an orphan it seems.

Grant's been patient with me, but much of what I learned about the camper to date was by experiment.

I thought the previous owner, a retired engineer who bought it new, would be a good source of information, turned out to have only used it as a mobile bedroom, and had not used the systems during his ownership, so has not been.

The gent didn't ever even light the hot water heater, or know that the HWH bypass valves were closed, evidently by the factory or the selling dealer, that they existed, or that one had to remove a cabinet drawer and reach around to move them (either did the factory, even after a couple exchanges, however). I now know these things.

Semi-funny story:

I was surprised when I made the "assumption" that because the bypass valves were closed, the HWT had been emptied, and that the camper had been "winterized." Because when I removed the nylon drain plug to verify, I was literally knocked on my ass by terrible smelling 20 year old water that must have been under 50+psi. I had opened the taps to vent pressure, but NOT again after I found the bypass valves closed. Doh! I knew better.

Anyway, that's why I am looking for better information sources here.

I guessed at function for the valve behind the little door because my Casita travel trailer has a similar valve (located elsewhere), and its purpose was to, when closed, prevent gray waste tank water only a few inches lower than the floor drain, from sloshing into the shower floor when driving on rough roads. Because it's now below freezing, I've refrained from experimenting by filling the shower with the blade valve in it's two positions.

I've found sometimes the best practical source of information is owners who have lived with the systems a while, which is why I was, in lieu or factory help, asking here.

I had the same question when we originally got our 1985 unit ... and I emailed them at bigfoot@bigfootrv.com ... they responded the same day. I remember that it had something to do with isolating the shower drain from the gray water tank when it gets relatively full. But, do email them for the full answer.

Thanks for hosting my photo!

Any opinion on the valve purpose?