myredracer wrote:
We have two grey tanks. No issues with us. I used to use a Valterra wye fitting but don't bother anymore. I always just lay the hose directly on the ground and dump the grey/black first and walk the hose contents into the sewer drain. Then move the hose over to the single grey tank and dump.
As mentioned, a simple of equalizing the tanks is to connect the 2 tanks together with with a garden hose. Use a fitting like below. Different versions/makes available. The one in the pic is nice as it makes removing and re-installing the end caps easy on the hands.

I know about using a garden hose to equalize the tank levels. Problem with that is it still leaves you with a lot of gray water to deal with downstream of the slide valves and in the garden hose. I actually have those caps already on the outlets.
What I was hoping to find is someone who has plumbed this up with hard pipe. I'm thinking of tapping into the existing tank drain pipes upstream of the slide valves and installing 2-3 inch hard pipe and then putting a slide valve in the new piping so I still have the option to separate the tanks if I want.
Anybody ever done anything like that? Thanks to all for the suggestions.