So in these cases, they are typically 1-2 nights tops, so we are not in danger of filling the black tank, (and if we did we could always dump it at the trailer dump). So I'm thinking about re-routing the grey water drains from both sinks right after they meet back in the bathroom, and re-routing it down the black tank vent instead of where it goes today to the grey water bypass just after the black tank valve.
I realize it's only a 20 Gallon tank, I'm okay with the size... we typically on a weekend trip only use 12 gallons of water at the sinks (I empty a 6 gallon gas/kerosene tank twice) and the black tank is never that full (as there are typically restrooms on site too). I have a brand new, modern valve on the black tank (not worried about the soaps destroying the seals)... give me reasons this is not a good idea? Why would this not work like I think it will?
The Barth I had before this had a single 40 Gallon tank in the rear that took both black and grey water in one place... seemed to work fine for them.
Also, keep in mind, I do not have the shower hooked up right now (supply lines), and even with this conversion if I choose to hook that back up again, the shower drain will continue to be hooked up to the same grey water bypass. That won't change with either option...
What I plan to do:
Option 1, leave the ability to use the bypass for sinks too. Cut the 2.25" drain line just after the "Y" where the bathroom trap drains into it. Install a new "Y" in it's place that routes over to the black stack vent line 3" to the left of the grey vent line. I would install 2 ball valves, one in place where the current connection runs to to the grey stack, and one on the new run to the black stack. This will allow me to choose which line I will use.
Option 2, permanently run to Black line and cap the old grey drain line on the stack.. This will be much simpler and cost effective. Just install a 45* bend after the cut, route to new y on the black stack, done.
Keep in mind, these two stacks merge into one, and join the stack from the kitchen sink before going up to a single shared vent up on the roof. So mixing the grey and black stacks will not cause additional odors, both sink lines are trapped at the source.
Thought and opinions?